First cut at API for ES6 ArrayBuffers

src/runtime.h

Index: src/runtime.h
diff --git a/src/runtime.h b/src/runtime.h
index 83e16412ebd8d0882bc72a5d87485fbff67aa0ce..eeaf02564dd106eb59962b5059dbf37cfae10da8 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -744,6 +744,16 @@ class Runtime : public AllStatic {
       Handle<Object> object,
       Handle<Object> key);
 
+  static bool SetupArrayBuffer(Isolate* isolate,
+                               Handle<JSArrayBuffer> array_buffer,
+                               void* data,
+                               size_t allocated_length);
+
+  static bool AllocateAndSetupArrayBuffer(
+      Isolate* isolate,
+      Handle<JSArrayBuffer> array_buffer,
+      size_t allocated_length);
+
   // Helper functions used stubs.
   static void PerformGC(Object* result);