Add experimental code behind a flag for Content Size Policy

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 26e6d0a1768a028b7e8fab6b4c62e8a64d574b45..24dd66b4b4cb7d7ee6fbbabf829edee2ab987ddf 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -52,6 +52,7 @@
 #include "content/browser/frame_host/render_frame_proxy_host.h"
 #include "content/browser/frame_host/render_widget_host_view_child_frame.h"
 #include "content/browser/host_zoom_map_impl.h"
+#include "content/browser/loader/content_size_frame_counter.h"
 #include "content/browser/loader/loader_io_thread_notifier.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/manifest/manifest_manager_host.h"
@@ -453,6 +454,7 @@ WebContentsImpl::WebContentsImpl(BrowserContext* browser_context)
   pepper_playback_observer_.reset(new PepperPlaybackObserver(this));
 #endif
   loader_io_thread_notifier_.reset(new LoaderIOThreadNotifier(this));
+  content_size_frame_counter_.reset(new ContentSizeFrameCounter(this));
   wake_lock_service_context_.reset(new WakeLockServiceContext(this));
 }