Enable creation of offscreen contexts which own their backing surface.

ui/gl/init/gl_factory_win.cc

Index: ui/gl/init/gl_factory_win.cc
diff --git a/ui/gl/init/gl_factory_win.cc b/ui/gl/init/gl_factory_win.cc
index 9a43d7ad1de775d134b0a6ac111395fd92ade1a5..898eaac926464bd10280304cb9951eef9cf3730d 100644
--- a/ui/gl/init/gl_factory_win.cc
+++ b/ui/gl/init/gl_factory_win.cc
@@ -95,14 +95,23 @@ 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 kGLImplementationEGLGLES2:
-      return InitializeGLSurface(new PbufferGLSurfaceEGL(size));
+      return new PbufferGLSurfaceEGL(size);
     case kGLImplementationDesktopGL:
-      return InitializeGLSurface(new PbufferGLSurfaceWGL(size));
+      return new PbufferGLSurfaceWGL(size);
     case kGLImplementationMockGL:
       return new GLSurfaceStub;
     default: