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_dll/cpptoc/browser_host_cpptoc.cc

@@ -9,7 +9,7 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=a84451b4f759f2a4a0fe673d90be1fb5053bfd1a$
+// $hash=516b55b7ea53e2de2b096e85ba0eb83f2a2693f3$
 //
 
 #include "libcef_dll/cpptoc/browser_host_cpptoc.h"
@@ -18,8 +18,10 @@
 #include "libcef_dll/cpptoc/drag_data_cpptoc.h"
 #include "libcef_dll/cpptoc/extension_cpptoc.h"
 #include "libcef_dll/cpptoc/navigation_entry_cpptoc.h"
+#include "libcef_dll/cpptoc/registration_cpptoc.h"
 #include "libcef_dll/cpptoc/request_context_cpptoc.h"
 #include "libcef_dll/ctocpp/client_ctocpp.h"
+#include "libcef_dll/ctocpp/dev_tools_message_observer_ctocpp.h"
 #include "libcef_dll/ctocpp/download_image_callback_ctocpp.h"
 #include "libcef_dll/ctocpp/navigation_entry_visitor_ctocpp.h"
 #include "libcef_dll/ctocpp/pdf_print_callback_ctocpp.h"
@@ -522,6 +524,81 @@ int CEF_CALLBACK browser_host_has_dev_tools(struct _cef_browser_host_t* self) {
   return _retval;
 }
 
+int CEF_CALLBACK
+browser_host_send_dev_tools_message(struct _cef_browser_host_t* self,
+                                    const void* message,
+                                    size_t message_size) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+  // Verify param: message; type: simple_byaddr
+  DCHECK(message);
+  if (!message)
+    return 0;
+
+  // Execute
+  bool _retval = CefBrowserHostCppToC::Get(self)->SendDevToolsMessage(
+      message, message_size);
+
+  // Return type: bool
+  return _retval;
+}
+
+int CEF_CALLBACK
+browser_host_execute_dev_tools_method(struct _cef_browser_host_t* self,
+                                      int message_id,
+                                      const cef_string_t* method,
+                                      struct _cef_dictionary_value_t* params) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+  // Verify param: method; type: string_byref_const
+  DCHECK(method);
+  if (!method)
+    return 0;
+  // Unverified params: params
+
+  // Execute
+  int _retval = CefBrowserHostCppToC::Get(self)->ExecuteDevToolsMethod(
+      message_id, CefString(method), CefDictionaryValueCppToC::Unwrap(params));
+
+  // Return type: simple
+  return _retval;
+}
+
+struct _cef_registration_t* CEF_CALLBACK
+browser_host_add_dev_tools_message_observer(
+    struct _cef_browser_host_t* self,
+    struct _cef_dev_tools_message_observer_t* observer) {
+  shutdown_checker::AssertNotShutdown();
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return NULL;
+  // Verify param: observer; type: refptr_diff
+  DCHECK(observer);
+  if (!observer)
+    return NULL;
+
+  // Execute
+  CefRefPtr<CefRegistration> _retval =
+      CefBrowserHostCppToC::Get(self)->AddDevToolsMessageObserver(
+          CefDevToolsMessageObserverCToCpp::Wrap(observer));
+
+  // Return type: refptr_same
+  return CefRegistrationCppToC::Wrap(_retval);
+}
+
 void CEF_CALLBACK
 browser_host_get_navigation_entries(struct _cef_browser_host_t* self,
                                     cef_navigation_entry_visitor_t* visitor,
@@ -1285,6 +1362,10 @@ CefBrowserHostCppToC::CefBrowserHostCppToC() {
   GetStruct()->show_dev_tools = browser_host_show_dev_tools;
   GetStruct()->close_dev_tools = browser_host_close_dev_tools;
   GetStruct()->has_dev_tools = browser_host_has_dev_tools;
+  GetStruct()->send_dev_tools_message = browser_host_send_dev_tools_message;
+  GetStruct()->execute_dev_tools_method = browser_host_execute_dev_tools_method;
+  GetStruct()->add_dev_tools_message_observer =
+      browser_host_add_dev_tools_message_observer;
   GetStruct()->get_navigation_entries = browser_host_get_navigation_entries;
   GetStruct()->set_mouse_cursor_change_disabled =
       browser_host_set_mouse_cursor_change_disabled;