Web Animations API: Deferred computation of interpolated values

Source/core/css/resolver/StyleResolver.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 737 matching lines @@
 
     loadPendingResources(state);
 
     didAccess();
 
     return state.takeStyle();
 }
 
 // This function is used by the WebAnimations JavaScript API method animate().
 // FIXME: Remove this when animate() switches away from resolution-dependent parsing.
-PassRefPtrWillBeRawPtr<AnimatableValue> StyleResolver::createAnimatableValueSnapshot(Element& element, CSSPropertyID property, CSSValue* value)
+PassRefPtrWillBeRawPtr<AnimatableValue> StyleResolver::applyAndSnapshotAnimatableValue(Element& element, CSSPropertyID property, CSSValue* value, RenderStyle* mutableStyle)
 {
-    // We use a fresh RenderStyle here because certain values (eg. background-position) won't always completely replace the previously applied property.
-    RefPtr<RenderStyle> style = element.renderStyle() ? RenderStyle::clone(element.renderStyle()) : RenderStyle::create();
+    RefPtr<RenderStyle> style;
+    if (mutableStyle)
+        style = mutableStyle;
+    else if (element.renderStyle())
+        style = RenderStyle::clone(element.renderStyle());
+    else
+        style = RenderStyle::create();
     StyleResolverState state(element.document(), &element);
     state.setStyle(style.get());
     state.fontBuilder().initForStyleResolve(state.document(), state.style(), state.useSVGZoomRules());
     StyleBuilder::applyProperty(property, state, value);
     return CSSAnimatableValueFactory::create(property, *style);
 }
 
 PassRefPtr<PseudoElement> StyleResolver::createPseudoElementIfNeeded(Element& parent, PseudoId pseudoId)
 {
     RenderObject* parentRenderer = parent.renderer();
@@ skipping 727 matching lines @@
     visitor->trace(m_viewportStyleResolver);
     visitor->trace(m_siblingRuleSet);
     visitor->trace(m_uncommonAttributeRuleSet);
     visitor->trace(m_watchedSelectorsRules);
     visitor->trace(m_treeBoundaryCrossingRules);
     visitor->trace(m_pendingStyleSheets);
     CSSFontSelectorClient::trace(visitor);
 }
 
 } // namespace WebCore