canvas.getContext with alpha:undefined should behave like alpha:true

Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp

Index: Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
diff --git a/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp b/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
index ae2010e3aeb3b76635d2e0bd02c4e8d8f775c8dd..b4d169b46ea9f2300edbed6777d4ecb1baeef88f 100644
--- a/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
+++ b/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
@@ -47,6 +47,16 @@
 
 namespace WebCore {
 
+static bool determineAlpha(v8::Handle<v8::Value> alphaValue)

[Justin Novosad, 2014/05/20 19:28:39]

We are going to need a more generic version of this function to handle all the
other attributes that suffer from the same bug with WebGL.  Suggestion:
template<T> static T readDictionaryValue(v8::Handle<v8::Value>, const T&
default)

+{
+    // WebIDL dictionary spec says that setting a dictionary value to undefined
+    // should result in the attribute retaining its default value.
+    if (isUndefinedOrNull(alphaValue))
+        return true;
+
+    return alphaValue->BooleanValue();
+}
+
 void V8HTMLCanvasElement::getContextMethodCustom(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     v8::Handle<v8::Object> holder = info.Holder();
@@ -61,7 +71,7 @@ void V8HTMLCanvasElement::getContextMethodCustom(const v8::FunctionCallbackInfo<
             v8::Handle<v8::Object> jsAttributes = info[1]->ToObject();
             v8::Handle<v8::String> alpha = v8AtomicString(isolate, "alpha");
             if (jsAttributes->Has(alpha))
-                webGLAttributes->setAlpha(jsAttributes->Get(alpha)->BooleanValue());
+                webGLAttributes->setAlpha(determineAlpha(jsAttributes->Get(alpha)));

[Justin Novosad, 2014/05/20 19:28:39]

Theroriginal bug was primarily about 2D canvas. If you are going to fix the
webGL case as well, you should add a test for it, and you should also fix the
other attributes that have the same problem.

             v8::Handle<v8::String> depth = v8AtomicString(isolate, "depth");
             if (jsAttributes->Has(depth))
                 webGLAttributes->setDepth(jsAttributes->Get(depth)->BooleanValue());
@@ -88,7 +98,7 @@ void V8HTMLCanvasElement::getContextMethodCustom(const v8::FunctionCallbackInfo<
             v8::Handle<v8::Object> jsAttributes = info[1]->ToObject();
             v8::Handle<v8::String> alpha = v8AtomicString(isolate, "alpha");
             if (jsAttributes->Has(alpha))
-                canvas2DAttributes->setAlpha(jsAttributes->Get(alpha)->BooleanValue());
+                canvas2DAttributes->setAlpha(determineAlpha(jsAttributes->Get(alpha)));
         }
         attributes = canvas2DAttributes;
     }