Avoid using declarations in headers which introduce symbol conflicts.

third_party/WebKit/Source/web/InspectorRenderingAgent.h

 // Copyright 2015 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 InspectorRenderingAgent_h
 #define InspectorRenderingAgent_h
 
 #include "core/inspector/InspectorBaseAgent.h"
 #include "core/inspector/protocol/Rendering.h"
 
 namespace blink {
 
 class InspectorOverlay;
 class WebLocalFrameImpl;
 class WebViewImpl;
 
 class InspectorRenderingAgent final
     : public InspectorBaseAgent<protocol::Rendering::Metainfo> {
   WTF_MAKE_NONCOPYABLE(InspectorRenderingAgent);
 
  public:
   static InspectorRenderingAgent* create(WebLocalFrameImpl*, InspectorOverlay*);
 
   // protocol::Dispatcher::PageCommandHandler implementation.
-  Response setShowPaintRects(bool) override;
-  Response setShowDebugBorders(bool) override;
-  Response setShowFPSCounter(bool) override;
-  Response setShowScrollBottleneckRects(bool) override;
-  Response setShowViewportSizeOnResize(bool) override;
+  protocol::Response setShowPaintRects(bool) override;
+  protocol::Response setShowDebugBorders(bool) override;
+  protocol::Response setShowFPSCounter(bool) override;
+  protocol::Response setShowScrollBottleneckRects(bool) override;
+  protocol::Response setShowViewportSizeOnResize(bool) override;
 
   // InspectorBaseAgent overrides.
-  Response disable() override;
+  protocol::Response disable() override;
   void restore() override;
 
   DECLARE_VIRTUAL_TRACE();
 
  private:
   InspectorRenderingAgent(WebLocalFrameImpl*, InspectorOverlay*);
-  Response compositingEnabled();
+  protocol::Response compositingEnabled();
   WebViewImpl* webViewImpl();
 
   Member<WebLocalFrameImpl> m_webLocalFrameImpl;
   Member<InspectorOverlay> m_overlay;
 };
 
 }  // namespace blink
 
 #endif  // !defined(InspectorRenderingAgent_h)