Fix TextInputClientMac related crashes of Fullscreen RenderWidget

content/renderer/text_input_client_observer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_TEXT_INPUT_CLIENT_OBSERVER_H_
 #define CONTENT_RENDERER_TEXT_INPUT_CLIENT_OBSERVER_H_
 
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "content/public/renderer/render_view_observer.h"
@@ skipping 18 matching lines @@
   explicit TextInputClientObserver(RenderWidget* render_widget);
   ~TextInputClientObserver() override;
 
   // IPC::Listener override.
   bool OnMessageReceived(const IPC::Message& message) override;
 
   // IPC::Sender override.
   bool Send(IPC::Message* message) override;
 
  private:
-  // The render widget corresponding to this TextInputClientObserver.
+  // Returns the WebFrameWidget for the RenderWidget owning this observer. It
+  // returns null if the RenderWidget corresponds to a fullscreen RenderWidget.
   blink::WebFrameWidget* GetWebFrameWidget() const;
 
   blink::WebLocalFrame* GetFocusedFrame() const;
 
 #if defined(ENABLE_PLUGINS)
   // Returns the currently focused pepper plugin on the page. The expectation is
   // that the focused pepper plugin is inside a frame whose local root is equal
   // to GetWebFrameWidget()->localRoot().
   PepperPluginInstanceImpl* GetFocusedPepperPlugin() const;
 #endif
 
   // IPC Message handlers:
   void OnStringAtPoint(gfx::Point point);
   void OnCharacterIndexForPoint(gfx::Point point);
   void OnFirstRectForCharacterRange(gfx::Range range);
   void OnStringForRange(gfx::Range range);
 
   // The RenderWidget owning this instance of the observer.
   RenderWidget* render_widget_;
 
   DISALLOW_COPY_AND_ASSIGN(TextInputClientObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_TEXT_INPUT_CLIENT_OBSERVER_H_