Force GPU switch with CGLSetVirtualScreen only for compositor

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index d72d5d241ee6ad18d6d046139476dea4fe4301fa..d9f0ff89f6bdef762bb1a09b211adf957d8d6797 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -18,9 +18,6 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
-#if defined(OS_MACOSX)
-#include "base/mac/scoped_cftyperef.h"
-#endif
 #include "base/memory/scoped_ptr.h"
 #include "base/string_number_conversions.h"
 #include "base/stringprintf.h"
@@ -61,7 +58,9 @@
 #include "ui/gl/gl_image.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
+
 #if defined(OS_MACOSX)
+#include "base/mac/scoped_cftyperef.h"

[Ken Russell (switch to Gerrit), 2013/04/09 00:48:58]

This change is not necessary for this CL; please undo it.

[ccameron, 2013/04/09 17:28:55]

Done.

 #include "ui/surface/io_surface_support_mac.h"
 #endif
 
@@ -2573,6 +2572,13 @@ bool GLES2DecoderImpl::Initialize(
     glPointParameteri(GL_POINT_SPRITE_COORD_ORIGIN, GL_LOWER_LEFT);
   }
 
+  // Only compositor contexts are known to use only the subset of GL
+  // that can be safely migrated between the iGPU and the dGPU. Mark
+  // those contexts as safe to forcibly transition between the GPUs.
+  // http://crbug.com/180876, http://crbug.com/227228
+  if (!offscreen)
+    context_->SetSafeToForceGpuSwitch();

[Ken Russell (switch to Gerrit), 2013/04/09 00:48:58]

Does this work when virtual contexts are being used? I don't know how the
service side code works in this configuration. Is the same context passed in to
multiple decoder instances?

[ccameron, 2013/04/09 17:28:55]

Good point -- I added support for virtual contexts. This will only work if all
virtualized contexts sharing a context agree about whether or not to allow
force-switching. It so-happens that they do ATM (because we only virtualize
compositor contexts on the Mac), but we may want to make this more stringent.

[Ken Russell (switch to Gerrit), 2013/04/09 17:42:03]

A TODO is needed. It is clear that if we virtualize accelerated 2D canvas's
context in with the compositor's context at some point in the future, things
will break. It's OK to merge the fix in its current form to M27.

+
   // Create a delegate to perform async pixel transfers.
   async_pixel_transfer_delegate_ =
       gfx::AsyncPixelTransferDelegate::Create(context.get());