Cleanup namespace usage in public/platform/{Web[P-W]*,linux/*}.h

public/platform/WebSerializedOrigin.h

 // Copyright 2014 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 WebSerializedOrigin_h
 #define WebSerializedOrigin_h
 
 #include "WebString.h"
 
-#if INSIDE_BLINK
-namespace blink { class SecurityOrigin; }
-#else
+#if !INSIDE_BLINK
 #include <url/origin.h>
 #endif
 
 namespace blink {
 
+class SecurityOrigin;
+
 // WebSerializedOrigin represents a serialized Web Origin specified in RFC6454.
 class WebSerializedOrigin {
 public:
     WebSerializedOrigin() : m_string("null") { }
 #if INSIDE_BLINK
-    BLINK_PLATFORM_EXPORT WebSerializedOrigin(const blink::SecurityOrigin&);
+    BLINK_PLATFORM_EXPORT WebSerializedOrigin(const SecurityOrigin&);
 #else
     WebSerializedOrigin(const url::Origin& origin) : m_string(WebString::fromUTF8(origin.string())) { }
     operator url::Origin() const { return url::Origin(m_string.utf8()); }
 #endif
 
     const WebString& string() const
     {
         return m_string;
     }
 
 private:
     const WebString m_string;
 };
 
 } // namespace blink
 
 #endif // #ifndef SerializedOrigin_h