This CL is refactor work. There is no behavior change.

The only change in codebase is replacing explicit usage of
StringBuilder in end code with public methods with the same
implementation.

It enables consistent access to output buffer from different printers
in various sources, this decoupling enables further work on gss
compiler.

Code Design:

It creates an abstract class CodePrinter to hold the output buffer and
related APIs to r/w the buffer, subclasses could only alter the buffer
through these APIs; this layer provides a complete control over the
pointers in output buffer.

All printers are extended from this base class and remove its own
output buffer.

CL also includes changes and cleanups for direct usage of output
buffer outside the css compiler itself.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=86326296