First cut at API for ES6 ArrayBuffers

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 3b8a9eadb385bd92b9c0d29659bd01fccdd2fe3b..9c933af697181d7f108adae1cc65e2eef63c9efa 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -693,6 +693,12 @@ class Heap {
   // Please note this does not perform a garbage collection.
   MUST_USE_RESULT MaybeObject* AllocateFunctionPrototype(JSFunction* function);
 
+  // Allocates a JS ArrayBuffer object.
+  // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
+  // failed.
+  // Please note this does not perform a garbage collection.
+  MUST_USE_RESULT MaybeObject* AllocateJSArrayBuffer();
+
   // Allocates a Harmony proxy or function proxy.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.