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..bc2622b5d98f97794f4cbb46126bcb2f2ac86f62 100644
--- a/Source/bindings/core/v8/V8BindingMacros.h
+++ b/Source/bindings/core/v8/V8BindingMacros.h
@@ -77,6 +77,24 @@ namespace blink {
     if (UNLIKELY(!var.prepare()))                  \
         return retVal;
 
+template <typename T>
+bool inline getValueFromMaybe(v8::Maybe<T> maybe, T& outVariable)

[Yuki, 2015/03/11 07:55:22]

nit: s/bool inline/inline bool/

[bashi, 2015/03/11 10:22:35]

Done.

+{
+    if (maybe.IsNothing())
+        return false;
+    outVariable = maybe.FromJust();
+    return true;
+}
+
+#define V8_CALL(outVariable, handle, methodCall, failureExpression)                    \

[Yuki, 2015/03/11 07:55:22]

nit: You cannot use 'break' in failureExpression.

It would be better to comment that users of this macro shouldn't use 'break' or
'continue' in failureExpression, or define this macro as:

if (...) {
  failureExpression;
} else

# The following semicolon ends the else clause.

[bashi, 2015/03/11 10:22:35]

Thanks, I took "if (...) { failureExpression; } else" approach.

+    do {                                                                               \
+        if (handle.IsEmpty() || !getValueFromMaybe(handle->methodCall, outVariable)) { \
+            do {                                                                       \

[Jens Widell, 2015/03/11 07:39:34]

This inner do{}while() is OTOH strictly speaking redundant. The
'failureExpression' parameter is already expanded inside {}.

[bashi, 2015/03/11 07:51:18]

Oh, right. Done.

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