Refactor oat file writing to give Dex2Oat more control.

This is the first step towards writing dex files to oat file
and mapping them from there for the actual AOT compilation.

Change-Id: Icb0d27487eaf6ba3a66c157e695f9bdc5bb9cf9a
diff --git a/compiler/file_output_stream.h b/compiler/file_output_stream.h
index 9dfbd7f..6917d83 100644
--- a/compiler/file_output_stream.h
+++ b/compiler/file_output_stream.h
@@ -27,11 +27,13 @@
  public:
   explicit FileOutputStream(File* file);
 
-  virtual ~FileOutputStream() {}
+  ~FileOutputStream() OVERRIDE {}
 
-  virtual bool WriteFully(const void* buffer, size_t byte_count);
+  bool WriteFully(const void* buffer, size_t byte_count) OVERRIDE;
 
-  virtual off_t Seek(off_t offset, Whence whence);
+  off_t Seek(off_t offset, Whence whence) OVERRIDE;
+
+  bool Flush() OVERRIDE;
 
  private:
   File* const file_;