Refactor Subzero initialization and add a browser callback handler.

src/IceTranslator.h

 //===- subzero/src/IceTranslator.h - ICE to machine code --------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the general driver class for translating ICE to
@@ skipping 56 matching lines @@
   /// Prefix to name unnamed names. Errors are put on Ostream.
   /// Returns true if there isn't a potential conflict.
   bool checkIfUnnamedNameSafe(const IceString &Name, const char *Kind,
                               const IceString &Prefix);
 
   uint32_t getNextSequenceNumber() { return NextSequenceNumber++; }
 
 protected:
   GlobalContext *Ctx;
   uint32_t NextSequenceNumber;
-  // Exit status of the translation. False is successful. True otherwise.
+  // ErrorCode of the translation.
   ErrorCode ErrorStatus;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETRANSLATOR_H