Add support for loading extensions (issue #1947)

- Add CefRequestContext::LoadExtension, CefExtension, CefExtensionHandler and
  related methods/interfaces.
- Add chrome://extensions-support that lists supported Chrome APIs.
- Add CefBrowserHost::SetAutoResizeEnabled and CefDisplayHandler::OnAutoResize
  to support browser resize based on preferred web contents size.
- views: Add support for custom CefMenuButton popups.
- cefclient: Run with `--load-extension=set_page_color` command-line flag for
  an extension loading example. Add `--use-views` on Windows and Linux for an
  even better example.

libcef/browser/extensions/extension_function_details.h

@@ -0,0 +1,114 @@
+// Copyright 2017 the Chromium Embedded Framework Authors. Portions copyright
+// 2014 The Chromium Authors. All rights reserved. Use of this source code is
+// governed by a BSD-style license that can be found in the LICENSE file.
+
+#ifndef CEF_LIBCEF_BROWSER_EXTENSIONS_EXTENSION_FUNCTION_DETAILS_H_
+#define CEF_LIBCEF_BROWSER_EXTENSIONS_EXTENSION_FUNCTION_DETAILS_H_
+
+#include "libcef/browser/browser_host_impl.h"
+
+#include "include/cef_extension.h"
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "ui/gfx/native_widget_types.h"
+
+class Profile;
+class UIThreadExtensionFunction;
+
+namespace content {
+class WebContents;
+}
+
+namespace extensions {
+
+// Provides CEF-specific details to UIThreadExtensionFunction implementations.
+// Based on chrome/browser/extensions/chrome_extension_function_details.h.
+class CefExtensionFunctionDetails {
+ public:
+  // Constructs a new ChromeExtensionFunctionDetails instance for |function|.
+  // This instance does not own |function| and must outlive it.
+  explicit CefExtensionFunctionDetails(UIThreadExtensionFunction* function);
+  ~CefExtensionFunctionDetails();
+
+  Profile* GetProfile() const;
+
+  // Get the "sender" browser that is hosting the extension. May return NULL
+  // during startup/shutdown.
+  CefRefPtr<CefBrowserHostImpl> GetSenderBrowser() const;
+
+  // Get the "current" browser that will be acted on by this extension function,
+  // if any. When mapping from a tabId use the GetBrowserForTabId* methods
+  // instead of calling this method directly.
+  //
+  // Many extension APIs operate relative to the browser that the calling code
+  // is running inside of. For example, popups and tabs all have a containing
+  // browser, but background pages and notification bubbles do not. Other APIs,
+  // like chrome.tabs.*, can act on either a specific browser (specified via the
+  // tabId parameter) or should allow the client to determine the most
+  // appropriate browser (for example, the browser that representing the
+  // foreground window).
+  //
+  // Incognito browsers should not be considered unless the calling extension
+  // has incognito access enabled. CEF does not internally enforce incognito
+  // status so we pass this flag to client callbacks for consideration.
+  //
+  // This method can return NULL if there is no matching browser, which can
+  // happen if only incognito windows are open, or early in startup or shutdown
+  // shutdown when there are no active windows.
+  CefRefPtr<CefBrowserHostImpl> GetCurrentBrowser() const;
+
+  // Returns true if the sender browser can access |target|. When mapping from a
+  // tabId use the GetBrowserForTabId* methods instead of calling this method
+  // directly.
+  bool CanAccessBrowser(CefRefPtr<CefBrowserHostImpl> target) const;
+
+  // Returns the browser matching |tab_id| or NULL if the browser cannot be
+  // found or does not have a WebContents. If |tab_id| is -1 the "current"
+  // browser will be returned. |error_message| can optionally be passed in and
+  // will be set with an appropriate message on error. This method should only
+  // be called one time per extension function and will check all necessary
+  // client permissions.
+  CefRefPtr<CefBrowserHostImpl> GetBrowserForTabIdFirstTime(
+      int tab_id,
+      std::string* error_message) const;
+
+  // Returns the browser matching |tab_id| or NULL if the browser cannot be
+  // found or does not have a WebContents. |tab_id| must be >= 0.
+  // |error_message| can optionally be passed in and will be set with an
+  // appropriate message on error. This method should be called only after
+  // GetBrowserForTabIdFirstTime() has succeeded for the same |tab_id|.
+  CefRefPtr<CefBrowserHostImpl> GetBrowserForTabIdAgain(
+      int tab_id,
+      std::string* error_message) const;
+
+  // Give the client a chance to handle |file|. |callback| will be executed
+  // once the file contents have been loaded. Returns false if the file is
+  // unhandled.
+  using LoadFileCallback =
+      base::OnceCallback<void(std::unique_ptr<std::string>)>;
+  bool LoadFile(const std::string& file, LoadFileCallback callback) const;
+
+  // Returns a pointer to the associated UIThreadExtensionFunction
+  UIThreadExtensionFunction* function() { return function_; }
+  const UIThreadExtensionFunction* function() const { return function_; }
+
+ protected:
+  CefRefPtr<CefExtension> GetCefExtension() const;
+
+ private:
+  // The function for which these details have been created. Must outlive the
+  // CefExtensionFunctionDetails instance.
+  UIThreadExtensionFunction* function_;
+
+  mutable CefRefPtr<CefExtension> cef_extension_;
+
+  // Verifies correct usage of GetBrowserForTabId* methods.
+  mutable bool get_browser_called_first_time_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(CefExtensionFunctionDetails);
+};
+
+}  // namespace extensions
+
+#endif  // CEF_LIBCEF_BROWSER_EXTENSIONS_EXTENSION_FUNCTION_DETAILS_H_