Load the GL_KHR_debug entry points and log messages they produce.

gpu/command_buffer/service/gpu_switches.cc

Index: gpu/command_buffer/service/gpu_switches.cc
diff --git a/gpu/command_buffer/service/gpu_switches.cc b/gpu/command_buffer/service/gpu_switches.cc
index 683a347ea852153a5497216b812334ec92be6dc2..d43a6733824266de00ffa9dc548ee97f19e76095 100644
--- a/gpu/command_buffer/service/gpu_switches.cc
+++ b/gpu/command_buffer/service/gpu_switches.cc
@@ -35,6 +35,9 @@ const char kEnableGPUDebugging[]            = "enable-gpu-debugging";
 // dlls.
 const char kEnableGPUServiceLoggingGPU[]    = "enable-gpu-service-logging";
 
+// Enable logging of GPU driver debug messages.
+const char kEnableGPUDriverDebugLogging[] = "enable-gpu-driver-debug-logging";
+
 // Turn off gpu program caching
 const char kDisableGpuProgramCache[]        = "disable-gpu-program-cache";