Remove content switches dependency in content/common/gpu.

gpu/command_buffer/client/gpu_switches.cc

 // Copyright (c) 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.
 
 #include "gpu/command_buffer/client/gpu_switches.h"
 
 namespace switches {
 
 // Enable GPU client logging.
 const char kEnableGPUClientLogging[]        = "enable-gpu-client-logging";
 
+// Enables TRACE for GL calls in the renderer.
+const char kEnableGpuClientTracing[]        = "enable-gpu-client-tracing";
+
 }  // namespace switches