Update V8 to r6101 as required by WebKit r74534

Change-Id: I7f84af8dd732f11898fd644b2c2b1538914cb78d
diff --git a/src/memory.h b/src/memory.h
index 27f32f7..901e78d 100644
--- a/src/memory.h
+++ b/src/memory.h
@@ -60,6 +60,10 @@
     return *reinterpret_cast<int*>(addr);
   }
 
+  static double& double_at(Address addr)  {
+    return *reinterpret_cast<double*>(addr);
+  }
+
   static Address& Address_at(Address addr)  {
     return *reinterpret_cast<Address*>(addr);
   }