Enable creation of offscreen contexts which own their backing surface.

ui/gl/init/gl_factory_mac.cc

Index: ui/gl/init/gl_factory_mac.cc
diff --git a/ui/gl/init/gl_factory_mac.cc b/ui/gl/init/gl_factory_mac.cc
index 243a7909b59e5ab9efa0e425a0a2079d6e55b868..da0d56f17a9ea7fb01af07281421da16467c3b88 100644
--- a/ui/gl/init/gl_factory_mac.cc
+++ b/ui/gl/init/gl_factory_mac.cc
@@ -115,14 +115,23 @@ scoped_refptr<GLSurface> CreateViewGLSurface(gfx::AcceleratedWidget window) {
 
 scoped_refptr<GLSurface> CreateOffscreenGLSurface(const gfx::Size& size) {
   TRACE_EVENT0("gpu", "gl::init::CreateOffscreenGLSurface");
+  scoped_refptr<GLSurface> surface =
+      CreateUninitializedOffscreenGLSurface(size);
+  if (surface && GetGLImplementation() != kGLImplementationMockGL)
+    InitializeGLSurface(surface);
+  return surface;
+}
+
+scoped_refptr<GLSurface> CreateUninitializedOffscreenGLSurface(
+    const gfx::Size& size) {
+  TRACE_EVENT0("gpu", "gl::init::CreateUninitializedOffscreenGLSurface");
   switch (GetGLImplementation()) {
     case kGLImplementationOSMesaGL:
-      return InitializeGLSurface(
-          new GLSurfaceOSMesa(GLSurface::SURFACE_OSMESA_RGBA, size));
+      return new GLSurfaceOSMesa(GLSurface::SURFACE_OSMESA_RGBA, size);
     case kGLImplementationDesktopGL:
     case kGLImplementationDesktopGLCoreProfile:
     case kGLImplementationAppleGL:
-      return InitializeGLSurface(new NoOpGLSurface(size));
+      return new NoOpGLSurface(size);
     case kGLImplementationMockGL:
       return new GLSurfaceStub;
     default: