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

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp

Index: third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
index 9edb535defc4a6739f1ea51fe171b6be192435b0..86a6c823694c740660f7502c252ddd10c768c8d3 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
@@ -26,6 +26,7 @@ OffscreenCanvasRenderingContext2D::OffscreenCanvasRenderingContext2D(OffscreenCa
 
 DEFINE_TRACE(OffscreenCanvasRenderingContext2D)
 {
+    visitor->trace(m_executionContext);
     OffscreenCanvasRenderingContext::trace(visitor);
     BaseRenderingContext2D::trace(visitor);
 }
@@ -87,6 +88,14 @@ RawPtr<ImageBitmap> OffscreenCanvasRenderingContext2D::transferToImageBitmap(Exc
 
 bool OffscreenCanvasRenderingContext2D::parseColorOrCurrentColor(Color& color, const String& colorString) const
 {
+    if (!m_executionContext)
+        const_cast<OffscreenCanvasRenderingContext2D*>(this)->m_executionContext = ScriptState::current(v8::Isolate::GetCurrent())->getExecutionContext();
+
+    DCHECK(m_executionContext);
+    if (m_executionContext->isWorkerGlobalScope()) {
+        return ::blink::parseColorOrCurrentColor(color, colorString, nullptr, m_executionContext->localCssValuePool());
+    }
+
     return ::blink::parseColorOrCurrentColor(color, colorString, nullptr);
 }