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/output/copy_output_request.h"
 #include "cc/output/copy_output_result.h"
 #include "cc/resources/texture_mailbox.h"
 #include "cc/test/paths.h"
 #include "cc/test/pixel_comparator.h"
 #include "cc/test/pixel_test_output_surface.h"
 #include "cc/test/pixel_test_software_output_device.h"
 #include "cc/test/pixel_test_utils.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "ui/gl/gl_implementation.h"
 #include "webkit/common/gpu/context_provider_in_process.h"
 #include "webkit/common/gpu/webgraphicscontext3d_in_process_command_buffer_impl.h"
 
 namespace cc {
 
 LayerTreePixelTest::LayerTreePixelTest()
     : pixel_comparator_(new ExactPixelComparator(true)),
       test_type_(GL_WITH_DEFAULT) {}
 
 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 210 matching lines @@
       out_pixels[dest_y + x + SK_G32_SHIFT/8] = pixels.get()[src_y + x + 1];
       out_pixels[dest_y + x + SK_B32_SHIFT/8] = pixels.get()[src_y + x + 2];
       out_pixels[dest_y + x + SK_A32_SHIFT/8] = pixels.get()[src_y + x + 3];
     }
   }
 
   return bitmap.Pass();
 }
 
 }  // namespace cc