Skeleton implementation of CSS Properties and Values API

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 79b8d1e384a4e59c1d01349676b847b377f7a4a1..0995b29c336435646b430970c1923fa6c0fe446c 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -1460,6 +1460,17 @@ void ComputedStyle::setVariable(const AtomicString& name, PassRefPtr<CSSVariable
     variables->setVariable(name, value);
 }
 
+void ComputedStyle::setRegisteredInheritedProperty(const AtomicString& name, const CSSValue* parsedValue)
+{
+    RefPtr<StyleVariableData>& variables = m_rareInheritedData.access()->variables;
+    DCHECK(variables);
+    if (!variables->hasOneRef())
+        variables = variables->copy();
+    DCHECK(!!parsedValue == !!variables->getVariable(name));

[meade_UTC10, 2016/09/06 04:52:07]

I don't really understand what this check is for, both parsedValue and
getVariable(name) must be null, or both must be not null? Why?

+    DCHECK(!(parsedValue && variables->getVariable(name)->needsVariableResolution()));

[meade_UTC10, 2016/09/06 04:52:07]

Is this one "you can clear a variable that still needs resolution, but you can't
set a new one (yet)"?

[Timothy Loh, 2016/09/06 08:21:17]

Both dchecks are sanity checks about the relation between the token stream value
(CSSVariableData) and the parsed value (CSSValue). For these to work we need to
guarantee some ordering of setting, I chose to always set the CSSVariableData
first. These two are alternate representations of the same data so they need to
be in sync.

First dcheck - There's a CSSVariableData if and only if there's a CSSValue
Second dcheck - If we have a value, we've already resolved the var references.
Maybe clearer if I write DCHECK(!(variables->getVariable(name) &&
variables->getVariable(name)->needsVariableResolution()))?

+    variables->setRegisteredInheritedProperty(name, parsedValue);
+}
+
 void ComputedStyle::removeVariable(const AtomicString& name)
 {
     RefPtr<StyleVariableData>& variables = m_rareInheritedData.access()->variables;