gpu: Use mojom API for recording log messages to the host.

content/common/gpu_host_messages.h

Index: content/common/gpu_host_messages.h
diff --git a/content/common/gpu_host_messages.h b/content/common/gpu_host_messages.h
index 34ea6e58d007115ca74ba73840ed6f9e92db3ea0..906f3587c6d06ed166426b40c32b21d32f010390 100644
--- a/content/common/gpu_host_messages.h
+++ b/content/common/gpu_host_messages.h
@@ -116,11 +116,5 @@ IPC_MESSAGE_CONTROL3(GpuHostMsg_Initialized,
 IPC_MESSAGE_CONTROL1(GpuHostMsg_GpuMemoryBufferCreated,
                      gfx::GpuMemoryBufferHandle /* handle */)
 
-// Message from GPU to add a GPU log message to the about:gpu page.
-IPC_MESSAGE_CONTROL3(GpuHostMsg_OnLogMessage,
-                     int /*severity*/,
-                     std::string /* header */,
-                     std::string /* message */)
-
 // Sent by the GPU process to indicate that a fields trial has been activated.
 IPC_MESSAGE_CONTROL1(GpuHostMsg_FieldTrialActivated, std::string /* name */)