Add a readbuffer function to d8, that reads a file into an ArrayBuffer.

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index c872f90958f48d16d21d1de86d694fa560bfe11d..23fdebcaf4043c018e49fc95d183ebe19c89cef8 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -308,6 +308,7 @@ class Shell : public i::AllStatic {
   static Handle<Value> DisableProfiler(const Arguments& args);
   static Handle<Value> Read(const Arguments& args);
   static Handle<Value> ReadBinary(const Arguments& args);
+  static Handle<Value> ReadBuffer(const Arguments& args);
   static Handle<String> ReadFromStdin();
   static Handle<Value> ReadLine(const Arguments& args) {
     return ReadFromStdin();