bindings: Use V8 MaybeLocal APIs in V8DeviceMotionEventCustom

Source/bindings/core/v8/V8MaybeLocalToLocal.h

Index: Source/bindings/core/v8/V8MaybeLocalToLocal.h
diff --git a/Source/bindings/core/v8/V8MaybeLocalToLocal.h b/Source/bindings/core/v8/V8MaybeLocalToLocal.h
new file mode 100644
index 0000000000000000000000000000000000000000..b55a592b0d47dcbc723840572ffa020890951858
--- /dev/null
+++ b/Source/bindings/core/v8/V8MaybeLocalToLocal.h
@@ -0,0 +1,44 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8MaybeLocalToLocal_h
+#define V8MaybeLocalToLocal_h
+
+#include <v8.h>
+
+namespace blink {
+
+template <typename T>
+struct UnwrapV8Local {
+};
+
+template <typename T>
+struct UnwrapV8Local<v8::Local<T>> {
+    typedef T type;
+};
+
+template <typename T>
+struct V8ToMaybeLocal {
+};
+
+template <>
+struct V8ToMaybeLocal<v8::Object> {
+    static v8::MaybeLocal<v8::Object> to(v8::Local<v8::Context> context, v8::Local<v8::Value> value)
+    {
+        return value->ToObject(context);
+    }
+};
+
+// Converts a V8 value to a specific V8 type using ToXXX() methods with checks.
+
+#define MAYBE_LOCAL_TO_LOCAL_VOID(context, inValue, outValue) do {                          \

[bashi, 2015/03/04 04:42:11]

I'm planning to add MAYBE_LOCAL_TO_LOCAL_DEFAULT(context, inValue, outValue,
failureReturnValue) which returns failureReturnValue on failure. The name could
be changed.

+    using ValueType = UnwrapV8Local<decltype(outValue)>::type;                              \
+    v8::MaybeLocal<ValueType> maybeValue = V8ToMaybeLocal<ValueType>::to(context, inValue); \
+    if (maybeValue.IsEmpty() || !maybeValue.ToLocal(&outValue))                             \
+        return;                                                                             \
+} while (false);

[Yuki, 2015/03/04 05:14:31]

You don't want the last semi-colon.

+
+} // namespace blink
+
+#endif // V8MaybeLocalToLocal_h