Revert of Remove the is_loading_ field from WebContentsImpl

content/test/web_contents_observer_sanity_checker.h

Index: content/test/web_contents_observer_sanity_checker.h
diff --git a/content/test/web_contents_observer_sanity_checker.h b/content/test/web_contents_observer_sanity_checker.h
index 8e57f73652a1c3356165731a682f0d6fd14d978d..78a52e9f4fe8c1117aa5cd43c280677ad51155e2 100644
--- a/content/test/web_contents_observer_sanity_checker.h
+++ b/content/test/web_contents_observer_sanity_checker.h
@@ -88,8 +88,6 @@
   bool OnMessageReceived(const IPC::Message& message,
                          RenderFrameHost* render_frame_host) override;
   void WebContentsDestroyed() override;
-  void DidStartLoading() override;
-  void DidStopLoading() override;
 
  private:
   explicit WebContentsObserverSanityChecker(WebContents* web_contents);
@@ -114,8 +112,6 @@
   // Remembers parents to make sure RenderFrameHost::GetParent() never changes.
   std::map<GlobalRoutingID, GlobalRoutingID> parent_ids_;
 
-  bool is_loading_;
-
   bool web_contents_destroyed_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsObserverSanityChecker);