[SPv2] Add createOpacityOnlyEffect test helper

third_party/WebKit/Source/platform/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//testing/test.gni")
 import("//third_party/WebKit/public/public_features.gni")
 import("//third_party/WebKit/Source/build/scripts/scripts.gni")
@@ skipping 1588 matching lines @@
     "testing/FontTestHelpers.h",
     "testing/FuzzedDataProvider.cpp",
     "testing/FuzzedDataProvider.h",
     "testing/GeometryPrinters.cpp",
     "testing/GeometryPrinters.h",
     "testing/HistogramTester.cpp",
     "testing/HistogramTester.h",
     "testing/MessageLoopForMojo.h",
     "testing/PaintPrinters.cpp",
     "testing/PaintPrinters.h",
+    "testing/PaintPropertyTestHelpers.h",
     "testing/PictureMatchers.cpp",
     "testing/PictureMatchers.h",
     "testing/PlatformTestPrinters.cpp",
     "testing/RuntimeEnabledFeaturesTestHelpers.h",
     "testing/TestPaintArtifact.cpp",
     "testing/TestPaintArtifact.h",
     "testing/TestingPlatformSupport.cpp",
     "testing/TestingPlatformSupport.h",
     "testing/TransformPrinters.cpp",
     "testing/TransformPrinters.h",
@@ skipping 449 matching lines @@
     "//third_party/WebKit/Source:inside_blink",
   ]
 
   deps = [
     ":test_support",
     "//cc/surfaces:surface_id",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }