Add toWebCoreString() / toWebCoreAtomicString() overloads taking a v8::String

Source/bindings/v8/custom/V8CanvasRenderingContext2DCustom.cpp

Index: Source/bindings/v8/custom/V8CanvasRenderingContext2DCustom.cpp
diff --git a/Source/bindings/v8/custom/V8CanvasRenderingContext2DCustom.cpp b/Source/bindings/v8/custom/V8CanvasRenderingContext2DCustom.cpp
index 362aacaea931fd4749ce8facd78c598a317bf28b..9a6325f288a96b537bd6e7d04005c4904c064fe1 100644
--- a/Source/bindings/v8/custom/V8CanvasRenderingContext2DCustom.cpp
+++ b/Source/bindings/v8/custom/V8CanvasRenderingContext2DCustom.cpp
@@ -78,7 +78,7 @@ void V8CanvasRenderingContext2D::strokeStyleAttributeSetterCustom(v8::Local<v8::
 {
     CanvasRenderingContext2D* impl = V8CanvasRenderingContext2D::toNative(info.Holder());
     if (value->IsString())
-        impl->setStrokeColor(toWebCoreString(value));
+        impl->setStrokeColor(toWebCoreString(value.As<v8::String>()));
     else
         impl->setStrokeStyle(toCanvasStyle(value, info.GetIsolate()));
 }
@@ -93,7 +93,7 @@ void V8CanvasRenderingContext2D::fillStyleAttributeSetterCustom(v8::Local<v8::St
 {
     CanvasRenderingContext2D* impl = V8CanvasRenderingContext2D::toNative(info.Holder());
     if (value->IsString())
-        impl->setFillColor(toWebCoreString(value));
+        impl->setFillColor(toWebCoreString(value.As<v8::String>()));
     else
         impl->setFillStyle(toCanvasStyle(value, info.GetIsolate()));
 }