Refactor Subzero initialization and add a browser callback handler.

src/IceCompiler.h

+//===- subzero/src/IceCompiler.h - Compiler driver --------------*- 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 driver for translating bitcode to native code.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SUBZERO_SRC_ICECOMPILER_H
+#define SUBZERO_SRC_ICECOMPILER_H
+
+#include "IceDefs.h"
+
+namespace llvm {
+class DataStreamer;
+}
+
+namespace Ice {
+
+class ClFlagsExtra;
+
+// A compiler driver. It may be called to handle a single compile request.
+class Compiler {
+  Compiler(const Compiler &) = delete;
+  Compiler &operator=(const Compiler &) = delete;
+
+public:
+  Compiler() {}
+
+  // Run the compiler with the given GlobalContext for compilation
+  // state.  Upon error, the Context's error status will be set.
+  void run(const ClFlagsExtra &ExtraFlags, GlobalContext &Ctx,
+           std::unique_ptr<llvm::DataStreamer> &&InputStream);
+};
+
+} // end of namespace Ice
+
+#endif // SUBZERO_SRC_ICECOMPILER_H