Add DrawingBuffer multisample resolve unit test.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferSoftwareRenderingTest.cpp

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferSoftwareRenderingTest.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferSoftwareRenderingTest.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferSoftwareRenderingTest.cpp
index 34ced16215fc082b9cb3e7dd739b72f4aef114e4..edcd8be52c9820136312cdf408d0288e0b8e36af 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferSoftwareRenderingTest.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBufferSoftwareRenderingTest.cpp
@@ -54,7 +54,8 @@ class DrawingBufferSoftwareRenderingTest : public Test {
             new WebGraphicsContext3DProviderSoftwareRenderingForTests(
                 std::move(gl)));
     drawing_buffer_ = DrawingBufferForTests::Create(
-        std::move(provider), nullptr, initial_size, DrawingBuffer::kPreserve);
+        std::move(provider), nullptr, initial_size, DrawingBuffer::kPreserve,
+        kDisableMultisampling);
     CHECK(drawing_buffer_);
   }