[bindings] Assert toDoubleSlow on v8::Value being a number.

R=jl@opera.com, haraken@chromium.org

Review URL: https://codereview.chromium.org/946293003

git-svn-id: svn://svn.chromium.org/blink/trunk@190651 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/bindings/core/v8/V8Binding.cpp

@@ -533,6 +533,7 @@ float toRestrictedFloat(v8::Handle<v8::Value> value, ExceptionState& exceptionSt
 
 double toDoubleSlow(v8::Handle<v8::Value> value, ExceptionState& exceptionState)
 {
+    ASSERT(!value->IsNumber());
     v8::Isolate* isolate = v8::Isolate::GetCurrent();
     v8::TryCatch block(isolate);
     double doubleValue = value->NumberValue();