Avoid using declarations in headers which introduce symbol conflicts.

third_party/WebKit/Source/web/InspectorEmulationAgent.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 InspectorEmulationAgent_h
 #define InspectorEmulationAgent_h
 
 #include "core/inspector/InspectorBaseAgent.h"
 #include "core/inspector/protocol/Emulation.h"
 #include "platform/WebTaskRunner.h"
@@ skipping 18 matching lines @@
    public:
     virtual ~Client() {}
 
     virtual void setCPUThrottlingRate(double rate) {}
   };
 
   static InspectorEmulationAgent* create(WebLocalFrameImpl*, Client*);
   ~InspectorEmulationAgent() override;
 
   // protocol::Dispatcher::EmulationCommandHandler implementation.
-  Response forceViewport(double x, double y, double scale) override;
-  Response resetViewport() override;
-  Response resetPageScaleFactor() override;
-  Response setPageScaleFactor(double) override;
-  Response setScriptExecutionDisabled(bool value) override;
-  Response setTouchEmulationEnabled(bool enabled,
-                                    Maybe<String> configuration) override;
-  Response setEmulatedMedia(const String&) override;
-  Response setCPUThrottlingRate(double) override;
-  Response setVirtualTimePolicy(const String& policy,
-                                Maybe<int> virtualTimeBudgetMs) override;
-  Response setDefaultBackgroundColorOverride(
-      Maybe<protocol::DOM::RGBA>) override;
+  protocol::Response forceViewport(double x, double y, double scale) override;
+  protocol::Response resetViewport() override;
+  protocol::Response resetPageScaleFactor() override;
+  protocol::Response setPageScaleFactor(double) override;
+  protocol::Response setScriptExecutionDisabled(bool value) override;
+  protocol::Response setTouchEmulationEnabled(
+      bool enabled,
+      protocol::Maybe<String> configuration) override;
+  protocol::Response setEmulatedMedia(const String&) override;
+  protocol::Response setCPUThrottlingRate(double) override;
+  protocol::Response setVirtualTimePolicy(
+      const String& policy,
+      protocol::Maybe<int> virtualTimeBudgetMs) override;
+  protocol::Response setDefaultBackgroundColorOverride(
+      protocol::Maybe<protocol::DOM::RGBA>) override;
 
   // InspectorBaseAgent overrides.
-  Response disable() override;
+  protocol::Response disable() override;
   void restore() override;
 
   DECLARE_VIRTUAL_TRACE();
 
  private:
   InspectorEmulationAgent(WebLocalFrameImpl*, Client*);
   WebViewImpl* webViewImpl();
   void virtualTimeBudgetExpired();
 
   Member<WebLocalFrameImpl> m_webLocalFrameImpl;
   Client* m_client;
   TaskHandle m_virtualTimeBudgetExpiredTaskHandle;
 };
 
 }  // namespace blink
 
 #endif  // !defined(InspectorEmulationAgent_h)