Enable creation of offscreen contexts which own their backing surface.

ui/gl/init/gl_factory_mac.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gl/init/gl_factory.h"
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/gl/gl_bindings.h"
@@ skipping 97 matching lines @@
     case kGLImplementationMockGL:
       return new GLSurfaceStub;
     default:
       NOTREACHED();
       return nullptr;
   }
 }
 
 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:
       NOTREACHED();
       return nullptr;
   }
 }
 
 }  // namespace init
 }  // namespace gl