Add initial chrome runtime support (see issue #2969)

Running `cefsimple --enable-chrome-runtime` will create and run a
Chrome browser window using the CEF app methods, and call
CefApp::OnContextInitialized as expected. CEF task methods also
work as expected in the main process. No browser-related methods or
callbacks are currently supported for the Chrome window, and the
application will exit when the last Chrome window closes.

The Chrome runtime requires resources.pak, chrome_100_percent.pak
and chrome_200_percent.pak files which were not previously built
with CEF. It shares the existing locales pak files which have been
updated to include additional Chrome-specific strings.

On Linux, the Chrome runtime requires GTK so use_gtk=true must be
specified via GN_DEFINES when building.

This change also refactors the CEF runtime, which can be tested in
the various supported modes by running:
$ cefclient
$ cefclient --multi-threaded-message-loop
$ cefclient --external-message-pump

patch/patches/linux_chrome_page_info_1099927.patch

@@ -0,0 +1,14 @@
+diff --git chrome/browser/ui/page_info/chrome_page_info_client.cc chrome/browser/ui/page_info/chrome_page_info_client.cc
+index e2972da9e548..2f356616ed97 100644
+--- chrome/browser/ui/page_info/chrome_page_info_client.cc
++++ chrome/browser/ui/page_info/chrome_page_info_client.cc
+@@ -17,5 +17,9 @@ std::unique_ptr<PageInfoDelegate> ChromePageInfoClient::CreatePageInfoDelegate(
+ }
+ 
+ int ChromePageInfoClient::GetJavaResourceId(int native_resource_id) {
++#if defined(OS_ANDROID)
+   return ResourceMapper::MapToJavaDrawableId(native_resource_id);
++#else
++  return 0;
++#endif
+ }