Introduce MaybeHandle to police exception checking in handlified code.

src/v8globals.h

 // Copyright 2012 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 110 matching lines @@
 class Descriptor;
 class DescriptorArray;
 class TransitionArray;
 class ExternalReference;
 class FixedArray;
 class FunctionTemplateInfo;
 class MemoryChunk;
 class SeededNumberDictionary;
 class UnseededNumberDictionary;
 class NameDictionary;
+template <typename T> class MaybeHandle;
 template <typename T> class Handle;
 class Heap;
 class HeapObject;
 class IC;
 class InterceptorInfo;
 class Isolate;
 class JSReceiver;
 class JSArray;
 class JSFunction;
 class JSObject;
@@ skipping 420 matching lines @@
 enum MinusZeroMode {
   TREAT_MINUS_ZERO_AS_ZERO,
   FAIL_ON_MINUS_ZERO
 };
 
 } }  // namespace v8::internal
 
 namespace i = v8::internal;
 
 #endif  // V8_V8GLOBALS_H_