Remove content switches dependency in content/common/gpu.

gpu/command_buffer/client/gpu_switches.cc

Index: gpu/command_buffer/client/gpu_switches.cc
diff --git a/gpu/command_buffer/client/gpu_switches.cc b/gpu/command_buffer/client/gpu_switches.cc
index 7f7abef864af060d321223d22b31e401da43eb30..8b2acaffafabaca51c48d20cbdd6a9e9db07003f 100644
--- a/gpu/command_buffer/client/gpu_switches.cc
+++ b/gpu/command_buffer/client/gpu_switches.cc
@@ -9,4 +9,7 @@ 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