Avoid using declarations in headers which introduce symbol conflicts.

third_party/WebKit/Source/core/inspector/InspectorBaseAgent.h

Index: third_party/WebKit/Source/core/inspector/InspectorBaseAgent.h
diff --git a/third_party/WebKit/Source/core/inspector/InspectorBaseAgent.h b/third_party/WebKit/Source/core/inspector/InspectorBaseAgent.h
index 718706f50ac1654d20babb8e7219c25482189067..2ad507f61a589772e479ae2cf8d49487f6579349 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorBaseAgent.h
+++ b/third_party/WebKit/Source/core/inspector/InspectorBaseAgent.h
@@ -42,9 +42,6 @@ namespace blink {
 
 class LocalFrame;
 
-using protocol::Maybe;
-using protocol::Response;
-
 class CORE_EXPORT InspectorAgent
     : public GarbageCollectedFinalized<InspectorAgent> {
  public:
@@ -85,7 +82,7 @@ class InspectorBaseAgent : public InspectorAgent,
     }
   }
 
-  Response disable() override { return Response::OK(); }
+  protocol::Response disable() override { return protocol::Response::OK(); }
 
   void dispose() override {
     disable();