[SPv175] Mask layers should have clip state equal to MaskClip

Otherwise there may be a clip inversion when drawing mask layers
for objects which include CSS clip.

Bug:822906

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I037304f4b6d777bf14aa1204631dac7cf24da139
Reviewed-on: https://chromium-review.googlesource.com/986718Reviewed-by: Tien-Ren Chen <trchen@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547084}

third_party/WebKit/Source/core/BUILD.gn

@@ -2055,6 +2055,7 @@ jumbo_source_set("unit_tests") {
     "paint/compositing/CompositedLayerMappingTest.cpp",
     "paint/compositing/CompositingInputsUpdaterTest.cpp",
     "paint/compositing/CompositingLayerAssignerTest.cpp",
+    "paint/compositing/CompositingLayerPropertyUpdaterTest.cpp",
     "paint/compositing/CompositingReasonFinderTest.cpp",
     "paint/compositing/PaintLayerCompositorTest.cpp",
     "paint/ng/ng_paint_fragment_test.cc",

third_party/WebKit/Source/core/paint/ObjectPaintProperties.h

@@ -98,6 +98,8 @@ class CORE_EXPORT ObjectPaintProperties {
   // |    Clips to a fragment's bounds.
   // |    This is only present for content under a fragmentation
   // |    container.
+  // | NOTE: for composited SPv1/SPv175 clip path clips, we move clip path clip
+  // |       below mask.
   // +-[ clip path clip ]
   //   |  Clip created by path-based CSS clip-path. Only exists if the
   //  /   clip-path is "simple" that can be applied geometrically. This and

third_party/WebKit/Source/core/paint/compositing/CompositingLayerPropertyUpdater.cpp

@@ -104,6 +104,8 @@ void CompositingLayerPropertyUpdater::Update(const LayoutObject& object) {
     const auto* properties = fragment_data.PaintProperties();
     DCHECK(properties && properties->Mask());
     state.SetEffect(properties->Mask());
+    state.SetClip(properties->MaskClip());
+
     mask_layer->SetLayerState(
         state, snapped_paint_offset + mask_layer->OffsetFromLayoutObject());
   }

third_party/WebKit/Source/core/paint/compositing/CompositingLayerPropertyUpdaterTest.cpp

+// Copyright 2018 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 "core/paint/PaintLayer.h"
+#include "core/paint/compositing/CompositedLayerMapping.h"
+#include "core/paint/compositing/CompositingLayerPropertyUpdater.h"
+#include "core/testing/CoreUnitTestHelper.h"
+#include "platform/graphics/GraphicsLayer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blink {
+
+class CompositingLayerPropertyUpdaterTest : public RenderingTest {
+ private:
+  void SetUp() override {
+    RenderingTest::SetUp();
+    EnableCompositing();
+  }
+};
+
+TEST_F(CompositingLayerPropertyUpdaterTest, MaskLayerState) {
+  SetBodyInnerHTML(R"HTML(
+    <div id=target style="position: absolute;
+        clip-path: polygon(-1px -1px, 86px 400px);
+        clip: rect(9px, -1px, -1px, 96px); will-change: transform">
+    </div>
+    )HTML");
+
+  PaintLayer* target =
+      ToLayoutBoxModelObject(GetLayoutObjectByElementId("target"))->Layer();
+  EXPECT_EQ(kPaintsIntoOwnBacking, target->GetCompositingState());
+  auto* mapping = target->GetCompositedLayerMapping();
+  auto* mask_layer = mapping->MaskLayer();
+
+  auto* paint_properties =
+      target->GetLayoutObject().FirstFragment().PaintProperties();
+  EXPECT_TRUE(paint_properties->CssClip());
+  EXPECT_TRUE(paint_properties->MaskClip());
+  EXPECT_EQ(paint_properties->MaskClip(),
+            mask_layer->layer_state_->state.Clip());
+}
+
+}  // namespace blink

third_party/WebKit/Source/platform/graphics/GraphicsLayer.h

@@ -433,6 +433,8 @@ class PLATFORM_EXPORT GraphicsLayer : public cc::LayerClient,
   std::unique_ptr<CompositedLayerRasterInvalidator> raster_invalidator_;
 
   base::WeakPtrFactory<GraphicsLayer> weak_ptr_factory_;
+
+  FRIEND_TEST_ALL_PREFIXES(CompositingLayerPropertyUpdaterTest, MaskLayerState);
 };
 
 // ObjectPaintInvalidatorWithContext::InvalidatePaintRectangleWithContext uses