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.

tests/ceftests/test_suite.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <string>
+#include <vector>
 
 #include "include/cef_command_line.h"
 #include "include/wrapper/cef_helpers.h"
@@ -26,6 +27,12 @@ class CefTestSuite {
   void GetSettings(CefSettings& settings) const;
   bool GetCachePath(std::string& path) const;
 
+  // Register a temp directory that should be deleted on shutdown.
+  void RegisterTempDirectory(const CefString& directory);
+
+  // Called after shutdown to delete any registered temp directories.
+  void DeleteTempDirectories();
+
   CefRefPtr<CefCommandLine> command_line() const { return command_line_; }
 
   // The return value from Run().
@@ -40,6 +47,9 @@ class CefTestSuite {
   CefScopedArgArray argv_;
   CefRefPtr<CefCommandLine> command_line_;
 
+  std::vector<CefString> temp_directories_;
+  base::Lock temp_directories_lock_;
+
   int retval_;
 };