bindings: Add a macro for V8 Maybe<T> APIs.

Source/bindings/core/v8/V8BindingMacros.h

Index: Source/bindings/core/v8/V8BindingMacros.h
diff --git a/Source/bindings/core/v8/V8BindingMacros.h b/Source/bindings/core/v8/V8BindingMacros.h
index 77a7faafd9a59fd952e4ad244a637f205fda3013..14601dd9b40db85bd74ac1a8d1d8ab8366a530d8 100644
--- a/Source/bindings/core/v8/V8BindingMacros.h
+++ b/Source/bindings/core/v8/V8BindingMacros.h
@@ -77,6 +77,22 @@ namespace blink {
     if (UNLIKELY(!var.prepare()))                  \
         return retVal;
 
+template <typename T>
+bool inline v8Maybe(v8::Maybe<T> maybe, T& outVariable)
+{
+    if (maybe.IsNothing())
+        return false;
+    outVariable = maybe.FromJust();
+    return true;
+}
+
+#define V8_MAYBE(outVariable, handle, methodCall, failureExpression)     \
+    if (handle.IsEmpty() || !v8Maybe(handle->methodCall, outVariable)) { \

[haraken, 2015/03/11 02:43:21]

Do we need the handle.IsEmpty() check? It could be a responsibility of the
caller side to make sure that the handle is not empty.

[bashi, 2015/03/11 03:46:26]

I think IsEmpty() check reduces many hand-written checks. I'd prefer having this
in this macro.

+        do {                                                             \
+            failureExpression;                                           \
+        } while (false);                                                 \
+    }
+
 } // namespace blink
 
 #endif // V8BindingMacros_h