Add DrawingBuffer multisample resolve unit test.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferTestHelpers.h

 // 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 "gpu/command_buffer/common/capabilities.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/gpu/DrawingBuffer.h"
 #include "platform/graphics/gpu/Extensions3DUtil.h"
 #include "public/platform/WebGraphicsContext3DProvider.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
 
 enum {
   kInitialWidth = 100,
   kInitialHeight = 100,
   kAlternateHeight = 50,
 };
 
 class DrawingBufferForTests : public DrawingBuffer {
  public:
   static PassRefPtr<DrawingBufferForTests> Create(
       std::unique_ptr<WebGraphicsContext3DProvider> context_provider,
       DrawingBuffer::Client* client,
       const IntSize& size,
-      PreserveDrawingBuffer preserve) {
+      PreserveDrawingBuffer preserve,
+      bool multisample_extension_supported) {

[Justin Novosad, 2017/04/12 19:22:15]

Use an enum instead of a bool here.  It's rule #10 of the blink style guide:
https://sites.google.com/a/chromium.org/dev/blink/coding-style

     std::unique_ptr<Extensions3DUtil> extensions_util =
         Extensions3DUtil::Create(context_provider->ContextGL());
     RefPtr<DrawingBufferForTests> drawing_buffer =
         AdoptRef(new DrawingBufferForTests(std::move(context_provider),
                                            std::move(extensions_util), client,
                                            preserve));
-    bool multisample_extension_supported = false;
     if (!drawing_buffer->Initialize(size, multisample_extension_supported)) {
       drawing_buffer->BeginDestruction();
       return nullptr;
     }
     return drawing_buffer.Release();
   }
 
   DrawingBufferForTests(
       std::unique_ptr<WebGraphicsContext3DProvider> context_provider,
       std::unique_ptr<Extensions3DUtil> extensions_util,
@@ skipping 349 matching lines @@
   GLbyte current_mailbox_byte_ = 0;
   IntSize most_recently_produced_size_;
   bool create_image_chromium_fail_ = false;
   GLuint current_image_id_ = 1;
   HashMap<GLuint, IntSize> texture_sizes_;
   HashMap<GLuint, IntSize> image_sizes_;
   HashMap<GLuint, GLuint> image_to_texture_map_;
 };
 
 }  // blink