Tidy ELF builder.

Don't do "if (ptr)". Use const. Use DISALLOW_COPY_AND_ASSIGN. Avoid public
member variables.
Move ValueObject to base and use in ELF builder.
Tidy VectorOutputStream to not use non-const reference arguments.

Change-Id: I2c727c3fc61769c3726de7cfb68b2d6eb4477e53
diff --git a/compiler/buffered_output_stream.h b/compiler/buffered_output_stream.h
index 75a3f24..bbc49df 100644
--- a/compiler/buffered_output_stream.h
+++ b/compiler/buffered_output_stream.h
@@ -23,7 +23,7 @@
 
 namespace art {
 
-class BufferedOutputStream : public OutputStream {
+class BufferedOutputStream FINAL : public OutputStream {
  public:
   explicit BufferedOutputStream(OutputStream* out);