Cleanup: Remove unneeded forward declarations in base, dbug, gpu, ipc, jingle, and media.

base/debug/trace_event_win.h

 // Copyright (c) 2011 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.
 
 // This file contains the Windows-specific declarations for trace_event.h.
 #ifndef BASE_DEBUG_TRACE_EVENT_WIN_H_
 #define BASE_DEBUG_TRACE_EVENT_WIN_H_
 #pragma once
 
 #include <string>
@@ skipping 100 matching lines @@
   CAPTURE_STACK_TRACE = 0x0001,
 };
 
 // The event format consists of:
 // The "name" string as a zero-terminated ASCII string.
 // The id pointer in the machine bitness.
 // The "extra" string as a zero-terminated ASCII string.
 // Optionally the stack trace, consisting of a DWORD "depth", followed
 //    by an array of void* (machine bitness) of length "depth".
 
-// Forward decl.
-struct TraceLogSingletonTraits;
-
-}  // nemspace debug
+}  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_TRACE_EVENT_WIN_H_