Add a flag to allow renderer to use software compositor when GL compositor doesn't work.

cc/test/layer_tree_pixel_test.cc

 // Copyright 2013 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 "cc/test/layer_tree_pixel_test.h"
 
 #include "base/path_service.h"
 #include "cc/layers/solid_color_layer.h"
 #include "cc/layers/texture_layer.h"
 #include "cc/output/copy_output_request.h"
@@ skipping 11 matching lines @@
 
 namespace cc {
 
 LayerTreePixelTest::LayerTreePixelTest()
     : pixel_comparator_(new ExactPixelComparator(true)),
       test_type_(GL_WITH_DEFAULT),
       pending_texture_mailbox_callbacks_(0) {}
 
 LayerTreePixelTest::~LayerTreePixelTest() {}
 
-scoped_ptr<OutputSurface> LayerTreePixelTest::CreateOutputSurface() {
+scoped_ptr<OutputSurface> LayerTreePixelTest::CreateOutputSurface(
+    bool fallback) {
   gfx::Vector2d viewport_offset(20, 10);
   gfx::Size surface_expansion_size(40, 60);
   scoped_ptr<PixelTestOutputSurface> output_surface;
 
   switch (test_type_) {
     case SOFTWARE_WITH_DEFAULT:
     case SOFTWARE_WITH_BITMAP: {
       scoped_ptr<PixelTestSoftwareOutputDevice> software_output_device(
           new PixelTestSoftwareOutputDevice);
       software_output_device->set_surface_expansion_size(
@@ skipping 325 matching lines @@
   return TextureMailbox(
       mailbox,
       base::Bind(&LayerTreePixelTest::ReleaseTextureMailbox,
                  base::Unretained(this),
                  base::Passed(&context3d),
                  texture_id),
       sync_point);
 }
 
 }  // namespace cc