As crazy as it is, redefinition of global properties should work

Furthermore, some of the ES6 tests do check for this behavior (this
fixes at least 9 of the tests in /test/built-ins/Object/, maybe more
elsewhere).

createMutableBinding used hasProperty(String*) to determine whether or
not it needs to actually define a property, which checks the prototype
chain.

This would be fine, but when writing values to properties, we used find() on
the InternalClass (which is equivilent to Object::hasOwnProperty), which
would fail as the property doesn't "really" exist on the object, it's somewhere
in the prototype chain. Thus, we'd incorrectly throw an exception in strict mode.

I see no regressions in ES5 from this change.

Change-Id: I3b097306f220a891955ec11eea860264746bc0ee
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/qml/jsruntime/qv4context.cpp

@@ -155,7 +155,7 @@ void ExecutionContext::createMutableBinding(String *name, bool deletable)
         ctx = ctx->d()->outer;
     }
 
-    if (activation->hasProperty(name))
+    if (activation->hasOwnProperty(name))
         return;
     ScopedProperty desc(scope);
     PropertyAttributes attrs(Attr_Data);

tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp

@@ -336,6 +336,7 @@ private slots:
     void instanceof();
     void constkw_data();
     void constkw();
+    void redefineGlobalProp();
 
 private:
 //    static void propertyVarWeakRefCallback(v8::Persistent<v8::Value> object, void* parameter);
@@ -8273,6 +8274,20 @@ void tst_qqmlecmascript::constkw()
     }
 }
 
+// Redefine a property found on the global object. It shouldn't throw.
+void tst_qqmlecmascript::redefineGlobalProp()
+{
+    {
+        QJSEngine engine;
+        QJSValue ret = engine.evaluate("\"use strict\"\n var toString = 1;");
+        QVERIFY2(!ret.isError(), qPrintable(ret.toString()));
+    }
+    {
+        QJSEngine engine;
+        QJSValue ret = engine.evaluate("var toString = 1;");
+        QVERIFY2(!ret.isError(), qPrintable(ret.toString()));
+    }
+}
 
 
 QTEST_MAIN(tst_qqmlecmascript)