Add support for direct DevTools protocol messaging (fixes issue #2961).

This change allows the client to directly send and receive DevTools
protocol messages (send method calls, and receive method results and
events) without requiring a DevTools front-end or remote-debugging
session.

This change includes additional supporting changes:
- Add a new CefRequestHandler::OnDocumentAvailableInMainFrame
  callback (see issue #1454).
- Add a CefParseJSON variant that accepts a UTF8-encoded buffer.
- Add a `--devtools-protocol-log-file=<path>` command-line flag for
  logging protocol messages sent to/from the DevTools front-end
  while it is displayed. This is useful for understanding existing
  DevTools protocol usage.
- Add a new "libcef_static_unittests" executable target to support
  light-weight unit tests of libcef_static internals (e.g. without
  requiring exposure via the CEF API). Files to be unittested are
  placed in the new "libcef_static_unittested" source_set which is
  then included by both the existing libcef_static library and the
  new unittests executable target.
- Linux: Remove use_bundled_fontconfig=false, which is no longer
  required and causes unittest build errors (see issue #2424).

This change also adds a cefclient demo for configuring offline mode
using the DevTools protocol (fixes issue #245). This is controlled
by the "Offline mode" context menu option and the `--offline`
command-line switch which will launch cefclient in offline mode. When
cefclient is offline all network requests will fail with
ERR_INTERNET_DISCONNECTED and navigator.onLine will return false when
called from JavaScript in any frame. This mode is per-browser so
newly created browser windows will have the default mode. Note that
configuring offline mode in this way will not update the Network tab
UI ("Throtting" option) in a displayed DevTools front-end instance.

libcef/browser/devtools/devtools_manager.cc

@@ -0,0 +1,200 @@
+// Copyright (c) 2020 The Chromium Embedded Framework Authors. All rights
+// reserved. Use of this source code is governed by a BSD-style license that
+// can be found in the LICENSE file.
+
+#include "libcef/browser/devtools/devtools_manager.h"
+
+#include "libcef/browser/devtools/devtools_controller.h"
+#include "libcef/browser/devtools/devtools_frontend.h"
+
+#include "content/public/browser/web_contents.h"
+
+namespace {
+
+// May be created on any thread but will be destroyed on the UI thread.
+class CefDevToolsRegistrationImpl : public CefRegistration,
+                                    public CefDevToolsController::Observer {
+ public:
+  explicit CefDevToolsRegistrationImpl(
+      CefRefPtr<CefDevToolsMessageObserver> observer)
+      : observer_(observer) {
+    DCHECK(observer_);
+  }
+
+  ~CefDevToolsRegistrationImpl() override {
+    CEF_REQUIRE_UIT();
+
+    // May be null if OnDevToolsControllerDestroyed was called.
+    if (!controller_)
+      return;
+
+    controller_->RemoveObserver(this);
+  }
+
+  void Initialize(CefBrowserHostImpl* browser,
+                  base::WeakPtr<CefDevToolsController> controller) {
+    CEF_REQUIRE_UIT();
+    DCHECK(browser && controller);
+    DCHECK(!browser_ && !controller_);
+    browser_ = browser;
+    controller_ = controller;
+
+    controller_->AddObserver(this);
+  }
+
+ private:
+  // CefDevToolsController::Observer methods:
+  bool OnDevToolsMessage(const base::StringPiece& message) override {
+    CEF_REQUIRE_UIT();
+    return observer_->OnDevToolsMessage(browser_, message.data(),
+                                        message.size());
+  }
+
+  void OnDevToolsMethodResult(int message_id,
+                              bool success,
+                              const base::StringPiece& result) override {
+    CEF_REQUIRE_UIT();
+    observer_->OnDevToolsMethodResult(browser_, message_id, success,
+                                      result.data(), result.size());
+  }
+
+  void OnDevToolsEvent(const base::StringPiece& method,
+                       const base::StringPiece& params) override {
+    CEF_REQUIRE_UIT();
+    observer_->OnDevToolsEvent(browser_, method.as_string(), params.data(),
+                               params.size());
+  }
+
+  void OnDevToolsAgentAttached() override {
+    CEF_REQUIRE_UIT();
+    observer_->OnDevToolsAgentAttached(browser_);
+  }
+
+  void OnDevToolsAgentDetached() override {
+    CEF_REQUIRE_UIT();
+    observer_->OnDevToolsAgentDetached(browser_);
+  }
+
+  void OnDevToolsControllerDestroyed() override {
+    CEF_REQUIRE_UIT();
+    browser_ = nullptr;
+    controller_.reset();
+  }
+
+  CefRefPtr<CefDevToolsMessageObserver> observer_;
+
+  CefBrowserHostImpl* browser_ = nullptr;
+  base::WeakPtr<CefDevToolsController> controller_;
+
+  IMPLEMENT_REFCOUNTING_DELETE_ON_UIT(CefDevToolsRegistrationImpl);
+  DISALLOW_COPY_AND_ASSIGN(CefDevToolsRegistrationImpl);
+};
+
+}  // namespace
+
+CefDevToolsManager::CefDevToolsManager(CefBrowserHostImpl* inspected_browser)
+    : inspected_browser_(inspected_browser), weak_ptr_factory_(this) {
+  CEF_REQUIRE_UIT();
+}
+
+CefDevToolsManager::~CefDevToolsManager() {
+  CEF_REQUIRE_UIT();
+}
+
+void CefDevToolsManager::ShowDevTools(const CefWindowInfo& windowInfo,
+                                      CefRefPtr<CefClient> client,
+                                      const CefBrowserSettings& settings,
+                                      const CefPoint& inspect_element_at) {
+  CEF_REQUIRE_UIT();
+  if (devtools_frontend_) {
+    if (!inspect_element_at.IsEmpty()) {
+      devtools_frontend_->InspectElementAt(inspect_element_at.x,
+                                           inspect_element_at.y);
+    }
+    devtools_frontend_->Focus();
+    return;
+  }
+
+  devtools_frontend_ = CefDevToolsFrontend::Show(
+      inspected_browser_, windowInfo, client, settings, inspect_element_at,
+      base::BindOnce(&CefDevToolsManager::OnFrontEndDestroyed,
+                     weak_ptr_factory_.GetWeakPtr()));
+}
+
+void CefDevToolsManager::CloseDevTools() {
+  CEF_REQUIRE_UIT();
+  if (!devtools_frontend_)
+    return;
+  devtools_frontend_->Close();
+}
+
+bool CefDevToolsManager::HasDevTools() {
+  CEF_REQUIRE_UIT();
+  return !!devtools_frontend_;
+}
+
+bool CefDevToolsManager::SendDevToolsMessage(const void* message,
+                                             size_t message_size) {
+  CEF_REQUIRE_UIT();
+  if (!message || message_size == 0)
+    return false;
+
+  if (!EnsureController())
+    return false;
+
+  return devtools_controller_->SendDevToolsMessage(
+      base::StringPiece(static_cast<const char*>(message), message_size));
+}
+
+int CefDevToolsManager::ExecuteDevToolsMethod(
+    int message_id,
+    const CefString& method,
+    CefRefPtr<CefDictionaryValue> params) {
+  CEF_REQUIRE_UIT();
+  if (method.empty())
+    return 0;
+
+  if (!EnsureController())
+    return 0;
+
+  if (params && params->IsValid()) {
+    CefDictionaryValueImpl* impl =
+        static_cast<CefDictionaryValueImpl*>(params.get());
+    CefValueController::AutoLock lock_scope(impl->controller());
+    return devtools_controller_->ExecuteDevToolsMethod(message_id, method,
+                                                       impl->GetValueUnsafe());
+  } else {
+    return devtools_controller_->ExecuteDevToolsMethod(message_id, method,
+                                                       nullptr);
+  }
+}
+
+// static
+CefRefPtr<CefRegistration> CefDevToolsManager::CreateRegistration(
+    CefRefPtr<CefDevToolsMessageObserver> observer) {
+  DCHECK(observer);
+  return new CefDevToolsRegistrationImpl(observer);
+}
+
+void CefDevToolsManager::InitializeRegistrationOnUIThread(
+    CefRefPtr<CefRegistration> registration) {
+  CEF_REQUIRE_UIT();
+
+  if (!EnsureController())
+    return;
+
+  static_cast<CefDevToolsRegistrationImpl*>(registration.get())
+      ->Initialize(inspected_browser_, devtools_controller_->GetWeakPtr());
+}
+
+void CefDevToolsManager::OnFrontEndDestroyed() {
+  devtools_frontend_ = nullptr;
+}
+
+bool CefDevToolsManager::EnsureController() {
+  if (!devtools_controller_) {
+    devtools_controller_.reset(
+        new CefDevToolsController(inspected_browser_->web_contents()));
+  }
+  return true;
+}