bindings: Use V8 MaybeLocal APIs in V8DeviceMotionEventCustom

Source/bindings/core/v8/V8BindingMacros.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 59 matching lines @@
 #define TOSTRING_VOID(type, var, value) \
     type var(value);                    \
     if (UNLIKELY(!var.prepare()))       \
         return;
 
 #define TOSTRING_DEFAULT(type, var, value, retVal) \
     type var(value);                               \
     if (UNLIKELY(!var.prepare()))                  \
         return retVal;
 
+// Use this macro to call V8 APIs which return MaybeLocal<T>.
+#define CALL_V8_MAYBELOCAL(outVariable, isolate, callExpression, exceptionState, failureReturnValue) \

[haraken, 2015/03/06 02:44:07]

Do we need the isolate parameter?

[haraken, 2015/03/06 02:44:07]

Nit: I'd prefer calling this CALL_V8, since we don't need to expose a concept of
MaybeLocal to bindings/.

[bashi, 2015/03/06 02:54:44]

It seems that v8::V8::IsExecutionTerminating() is deprecated (since it uses
Isolate::GetCurrent()).

[bashi, 2015/03/06 02:54:44]

I'm fine with dropping _MAYBELOCAL, but what the name should be for Maybe<T>?
https://code.google.com/p/chromium/codesearch#chromium/src/v8/include/v8.h&l=...

+    {                                                                                                \
+        v8::TryCatch block;                                                                          \

[haraken, 2015/03/06 02:44:07]

Why do we need this TryCatch block?

- It's heavy so we need to avoid it as much as possible.
- If we just want to rethrow, we don't need the TryCatch block?

[bashi, 2015/03/06 02:54:44]

Yeah, this is my concern, but...
How can we detect a JavaScript exception without TryCatch? IIUC, ExceptionState
does nothing with detecting JS exceptions (I might be wrong here, though).

[Yuki, 2015/03/06 04:30:03]

Maybe, we'd better ask V8 team to make ToLocal() return false whenever an
exception is thrown.

[bashi, 2015/03/06 05:11:37]

@dcarney, WDYT?

[haraken, 2015/03/06 05:30:51]

I'm confused. ToLocal() already returns false when an exception is thrown,
because MaybeLocal is an empty handle when an exception is thrown, isn't it?

+        if ((callExpression).ToLocal(&outVariable)) {                                                \

[Yuki, 2015/03/06 04:30:03]

Did you mean?:
  if (!(...))

I thought that ToLocal returns true on success and false on failure.

[bashi, 2015/03/06 05:11:37]

ToLocal() returns true when the MaybeLocal<T> is empty.

That's said, I thought exactly the same as you, and AFAIK, it did return true on
success... I'm not sure the reason of this change.

+            if (isolate->IsExecutionTerminating())                                                   \
+                return failureReturnValue;                                                           \
+            if (block.HasCaught())                                                                   \
+                exceptionState.rethrowV8Exception(block.Exception());                                \
+            return failureReturnValue;                                                               \
+        }                                                                                            \
+    }
+
 } // namespace blink
 
 #endif // V8BindingMacros_h