Remove WebContents::InsertCSS since it is unused

content/renderer/render_frame_impl.h

 // Copyright 2013 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_RENDER_FRAME_IMPL_H_
 #define CONTENT_RENDERER_RENDER_FRAME_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 773 matching lines @@
   void OnDelete();
   void OnSelectAll();
   void OnSelectRange(const gfx::Point& base, const gfx::Point& extent);
   void OnAdjustSelectionByCharacterOffset(int start_adjust, int end_adjust);
   void OnUnselect();
   void OnMoveRangeSelectionExtent(const gfx::Point& point);
   void OnReplace(const base::string16& text);
   void OnReplaceMisspelling(const base::string16& text);
   void OnCopyImageAt(int x, int y);
   void OnSaveImageAt(int x, int y);
-  void OnCSSInsertRequest(const std::string& css);
   void OnAddMessageToConsole(ConsoleMessageLevel level,
                              const std::string& message);
   void OnJavaScriptExecuteRequest(const base::string16& javascript,
                                   int id,
                                   bool notify_result);
   void OnJavaScriptExecuteRequestForTests(const base::string16& javascript,
                                           int id,
                                           bool notify_result,
                                           bool has_user_gesture);
   void OnJavaScriptExecuteRequestInIsolatedWorld(const base::string16& jscript,
@@ skipping 486 matching lines @@
   mojom::FrameHostPtr frame_host_;
 
   base::WeakPtrFactory<RenderFrameImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderFrameImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_FRAME_IMPL_H_