Ensure baseComputedStyle optimisation is cleared during registered custom property animations

third_party/WebKit/Source/web/tests/AnimationSimTest.cpp

Index: third_party/WebKit/Source/web/tests/AnimationSimTest.cpp
diff --git a/third_party/WebKit/Source/web/tests/AnimationSimTest.cpp b/third_party/WebKit/Source/web/tests/AnimationSimTest.cpp
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+++ b/third_party/WebKit/Source/web/tests/AnimationSimTest.cpp
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+// Copyright 2017 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/animation/ElementAnimation.h"
+#include "core/css/PropertyDescriptor.h"
+#include "core/css/PropertyRegistration.h"
+#include "public/web/WebScriptSource.h"
+#include "web/WebLocalFrameImpl.h"
+#include "web/tests/sim/SimCompositor.h"
+#include "web/tests/sim/SimDisplayItemList.h"
+#include "web/tests/sim/SimRequest.h"
+#include "web/tests/sim/SimTest.h"
+#include "wtf/CurrentTime.h"
+
+namespace blink {
+
+class AnimationSimTest : public SimTest {};
+
+TEST_F(AnimationSimTest, CustomPropertyBaseComputedStyle) {
+  // This is a regression test for bug where custom property animations failed
+  // to disable the baseComputedStyle optimisation. When custom property
+  // animations are in effect we lose the guarantee that the baseComputedStyle
+  // optimisation relies on where the non-animated style rules always produce
+  // the same ComputedStyle. This is not the case if they use var() references
+  // to custom properties that are being animated.
+  // The bug was that we never cleared the existing baseComputedStyle during a
+  // custom property animation so the stale ComputedStyle object would hang
+  // around and not be valid in the exit frame of the next custom property
+  // animation.
+
+  RuntimeEnabledFeatures::setCSSVariables2Enabled(true);
+  RuntimeEnabledFeatures::setCSSAdditiveAnimationsEnabled(true);
+  RuntimeEnabledFeatures::setStackedCSSPropertyAnimationsEnabled(true);
+
+  webView().page()->animator().clock().disableSyntheticTimeForTesting();
+
+  SimRequest mainResource("https://example.com/", "text/html");
+  loadURL("https://example.com/");
+  mainResource.complete("<div id=\"target\"></div>");
+
+  Element* target = document().getElementById("target");
+
+  // CSS.registerProperty({
+  //   name: '--x',
+  //   syntax: '<percentage>',
+  //   initialValue: '0%',
+  // })
+  DummyExceptionStateForTesting exceptionState;
+  PropertyDescriptor propertyDescriptor;
+  propertyDescriptor.setName("--x");
+  propertyDescriptor.setSyntax("<percentage>");
+  propertyDescriptor.setInitialValue("0%");
+  PropertyRegistration::registerProperty(&document(), propertyDescriptor,
+                                         exceptionState);
+  EXPECT_FALSE(exceptionState.hadException());
+
+  // target.style.setProperty('--x', '100%');
+  target->style()->setProperty("--x", "100%", emptyString, exceptionState);
+  EXPECT_FALSE(exceptionState.hadException());
+
+  // target.animate({'--x': '100%'}, 1000);
+  RefPtr<StringKeyframe> keyframe = StringKeyframe::create();
+  keyframe->setCSSPropertyValue("--x", document().propertyRegistry(), "100%",
+                                document().elementSheet().contents());
+  StringKeyframeVector keyframes;
+  keyframes.push_back(keyframe.release());
+  Timing timing;
+  timing.iterationDuration = 1;  // Seconds.
+  ElementAnimation::animate(
+      *target, StringKeyframeEffectModel::create(keyframes), timing);
+
+  // This sets the baseComputedStyle on the animation exit frame.
+  compositor().beginFrame(1);
+  compositor().beginFrame(1);
+
+  // target.style.setProperty('--x', '0%');
+  target->style()->setProperty("--x", "0%", emptyString, exceptionState);
+  EXPECT_FALSE(exceptionState.hadException());
+
+  // target.animate({'--x': '100%'}, 1000);
+  keyframe = StringKeyframe::create();
+  keyframe->setCSSPropertyValue("--x", document().propertyRegistry(), "100%",
+                                document().elementSheet().contents());
+  keyframes.clear();
+  keyframes.push_back(keyframe.release());
+  timing = Timing::defaults();
+  timing.iterationDuration = 1;  // Seconds.
+  ElementAnimation::animate(
+      *target, StringKeyframeEffectModel::create(keyframes), timing);
+
+  // This (previously) would not clear the existing baseComputedStyle and would
+  // crash on the equality assertion in the exit frame when it tried to update
+  // it.
+  compositor().beginFrame(1);
+  compositor().beginFrame(1);
+}
+
+}  // namespace blink