Make CSSValuePool thread local to ensure correct parsing in colors on workers

third_party/WebKit/Source/core/dom/ExecutionContext.cpp

Index: third_party/WebKit/Source/core/dom/ExecutionContext.cpp
diff --git a/third_party/WebKit/Source/core/dom/ExecutionContext.cpp b/third_party/WebKit/Source/core/dom/ExecutionContext.cpp
index a190bcd84b65555f3a930c0c1d95ee16ebf591c1..0cc85456837f076a4b3104afa4884f89cacb375e 100644
--- a/third_party/WebKit/Source/core/dom/ExecutionContext.cpp
+++ b/third_party/WebKit/Source/core/dom/ExecutionContext.cpp
@@ -273,9 +273,22 @@ void ExecutionContext::removeURLFromMemoryCache(const KURL& url)
     memoryCache()->removeURLFromCache(url);
 }
 
+CSSValuePool* ExecutionContext::localCssValuePool()
+{
+    // Local CSS caches are only for worker threads.
+    if (!this->isWorkerGlobalScope())
+        return nullptr;
+
+    // Lazily initialization to avoid unnecessary CSS caches.
+    if (!m_localCssValuePool)
+        m_localCssValuePool = new CSSValuePool();
+    return m_localCssValuePool;
+}
+
 DEFINE_TRACE(ExecutionContext)
 {
     visitor->trace(m_publicURLManager);
+    visitor->trace(m_localCssValuePool);
     ContextLifecycleNotifier::trace(visitor);
     Supplementable<ExecutionContext>::trace(visitor);
 }