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.

patch/patch.cfg

@@ -75,6 +75,12 @@ patches = [
     # Support creation of captionless windows with resizable borders.
     # https://bitbucket.org/chromiumembedded/cef/issues/1749
     #
+    # Windows: When |params.remove_standard_frame| is true remove WS_CAPTION
+    # and WS_SYSMENU styles. Otherwise Windows 10 enforces a minimum window
+    # width of ~116 units that cannot be overridden.
+    # Linux: Allow creation of activatable menu windows.
+    # https://bitbucket.org/chromiumembedded/cef/issues/1947
+    #
     # Support configuration of RWHVGuest device scale factor.
     # https://bitbucket.org/chromiumembedded/cef/issues/2078
     'name': 'views_widget_180_1481_1565_1677_1749',
@@ -327,4 +333,12 @@ patches = [
     # https://bugs.chromium.org/p/chromium/issues/detail?id=747693
     'name': 'mac_build_747693',
   },
+  {
+    # Changes necessary to support for chrome extensions:
+    # (a) Add a new ExtensionHost constructor that allows CEF to create the
+    #     WebContents.
+    # (b) Always create ProcessManager using CEF's BrowserContextImpl.
+    # https://bitbucket.org/chromiumembedded/cef/issues/1947
+    'name': 'extensions_1947',
+  },
 ]