Fix Win64 build

src/runtime.cc

 // 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 833 matching lines @@
 
     memset(data, 0, allocated_length);
   } else {
     data = NULL;
   }
   holder->set_backing_store(data);
 
   Object* byte_length;
   {
     MaybeObject* maybe_byte_length =
-        isolate->heap()->NumberFromDouble(allocated_length);
+        isolate->heap()->NumberFromDouble(
+            static_cast<double>(allocated_length));
     if (!maybe_byte_length->ToObject(&byte_length)) return maybe_byte_length;
   }
   CHECK(byte_length->IsSmi() || byte_length->IsHeapNumber());
   holder->set_byte_length(byte_length);
 
   v8::Isolate* external_isolate = reinterpret_cast<v8::Isolate*>(isolate);
   v8::Handle<Object> external_holder(*holder);
   Persistent<Object> weak_handle = Persistent<Object>::New(
       external_isolate, external_holder);
   weak_handle.MakeWeak(external_isolate, data, ArrayBufferWeakCallback);
@@ skipping 12285 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal