Support dynamic switching between integrated and discrete GPUs on Mac OS X.

ui/gfx/gl/gl_context_mac.cc

Index: ui/gfx/gl/gl_context_mac.cc
===================================================================
--- ui/gfx/gl/gl_context_mac.cc	(revision 104937)
+++ ui/gfx/gl/gl_context_mac.cc	(working copy)
@@ -4,6 +4,7 @@
 
 #include "base/basictypes.h"
 #include "base/logging.h"
+#include "base/mac/mac_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "third_party/mesa/MesaLib/include/GL/osmesa.h"
 #include "ui/gfx/gl/gl_bindings.h"
@@ -20,18 +21,19 @@
 
 scoped_refptr<GLContext> GLContext::CreateGLContext(
     GLShareGroup* share_group,
-    GLSurface* compatible_surface) {
+    GLSurface* compatible_surface,
+    GpuPreference gpu_preference) {
   switch (GetGLImplementation()) {
     case kGLImplementationDesktopGL: {
       scoped_refptr<GLContext> context(new GLContextCGL(share_group));
-      if (!context->Initialize(compatible_surface))
+      if (!context->Initialize(compatible_surface, gpu_preference))
         return NULL;
 
       return context;
     }
     case kGLImplementationOSMesaGL: {
       scoped_refptr<GLContext> context(new GLContextOSMesa(share_group));
-      if (!context->Initialize(compatible_surface))
+      if (!context->Initialize(compatible_surface, gpu_preference))
         return NULL;
 
       return context;
@@ -44,4 +46,10 @@
   }
 }
 
+bool GLContext::SupportsDualGpus() {
+  // TODO(kbr): the precision of this query could be improved, in
+  // particular to detect single-GPU systems.

[Mark Mentovai, 2011/10/12 00:48:18]

This is the one thing I think we can do way better on. Are you planning to
address this in a quick follow-up?

[Ken Russell (switch to Gerrit), 2011/10/12 01:16:36]

I agree, this could be done better. Unfortunately I don't know how to reliably
detect the dual-GPU case and so can't promise a quick fix (i.e., by the M16
branch point), though I am happy to file a follow-on bug now and reference it in
the comment if you like.

Note that the main side-effect is only slightly less efficient startup and
shutdown of WebGL content on single-GPU Lion (and later) systems.

+  return base::mac::IsOSLionOrLater();
+}
+
 }  // namespace gfx