Re-land of http://codereview.chromium.org/6094009 with Mac build fix....

chrome/common/gpu_messages_internal.h

Index: chrome/common/gpu_messages_internal.h
===================================================================
--- chrome/common/gpu_messages_internal.h	(revision 70681)
+++ chrome/common/gpu_messages_internal.h	(working copy)
@@ -25,6 +25,14 @@
 //------------------------------------------------------------------------------
 // GPU Messages
 // These are messages from the browser to the GPU process.
+
+// Tells the GPU process to initialize itself. The browser explicitly
+// requests this be done so that we are guaranteed that the channel is set
+// up between the browser and GPU process before doing any work that might
+// potentially crash the GPU process. Detection of the child process
+// exiting abruptly is predicated on having the IPC channel set up.
+IPC_MESSAGE_CONTROL0(GpuMsg_Initialize)
+
 // Tells the GPU process to create a new channel for communication with a
 // given renderer.  The channel name is returned in a
 // GpuHostMsg_ChannelEstablished message.  The renderer ID is passed so that