Force flattening for elements with non-initial value of opacity

third_party/WebKit/Source/core/style/ComputedStyle.cpp

Index: third_party/WebKit/Source/core/style/ComputedStyle.cpp
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.cpp b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
index aedf11027a24dc5cfa9a9215552689f78ead0496..1ead5d7f4ebcd25ae4b2c935431fbed3037d82e0 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -1259,6 +1259,15 @@ CSSTransitionData& ComputedStyle::accessTransitions()
     return *rareNonInheritedData->m_transitions;
 }
 
+ETransformStyle3D ComputedStyle::usedTransformStyle3D() const
+{
+    // Quick rejection. Technically no-op.
+    if (transformStyle3D() == TransformStyle3DFlat)

[chrishtr, 2016/06/15 16:06:41]

Does this really matter for performance?

[trchen, 2016/06/18 00:27:09]

I don't have numbers, but checking will-change list can be potentially
expensive.

[chrishtr, 2016/06/18 08:22:53]

All this saves is a call to hasGroupingProperty. I don't think it's worth it.

+        return TransformStyle3DFlat;
+
+    return hasGroupingProperty() ? TransformStyle3DFlat : transformStyle3D();
+}
+
 const Font& ComputedStyle::font() const { return inherited->font; }
 const FontMetrics& ComputedStyle::getFontMetrics() const { return inherited->font.getFontMetrics(); }
 const FontDescription& ComputedStyle::getFontDescription() const { return inherited->font.getFontDescription(); }