Add experimental code behind a flag for Content Size Policy

content/browser/web_contents/web_contents_impl.h

Index: content/browser/web_contents/web_contents_impl.h
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index 91226f87578512b1516706f852f25c009a18c5af..a75531d0a894bbf23d284e5de88a37b2e0b3f8f8 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -54,6 +54,7 @@ struct ViewHostMsg_DateTimeDialogValue_Params;
 namespace content {
 class BrowserPluginEmbedder;
 class BrowserPluginGuest;
+class ContentSizeFrameCounter;
 class DateTimeChooserAndroid;
 class DownloadItem;
 class FindRequestManager;
@@ -751,6 +752,10 @@ class CONTENT_EXPORT WebContentsImpl
     return media_web_contents_observer_.get();
   }
 
+  ContentSizeFrameCounter* content_size_frame_counter() {
+    return content_size_frame_counter_.get();
+  }
+
   // Update the web contents visibility.
   void UpdateWebContentsVisibility(bool visible);
 
@@ -1388,6 +1393,10 @@ class CONTENT_EXPORT WebContentsImpl
   // Notifies ResourceDispatcherHostImpl of various events related to loading.
   std::unique_ptr<LoaderIOThreadNotifier> loader_io_thread_notifier_;
 
+  // UI thread state needed for the ContentSizeResourceHandlerManager to
+  // properly enforce size policies.
+  std::unique_ptr<ContentSizeFrameCounter> content_size_frame_counter_;
+
   // Manages media players, CDMs, and power save blockers for media.
   std::unique_ptr<MediaWebContentsObserver> media_web_contents_observer_;