Significantly cleans up the ImageWriter Operation class and subclasses.

* Moved Operations to be in CPS for stage isolation.
* Updates unit tests to use isolated stages.
* Adds unit tests for uncovered stages.
* Cleans up temporary file handling.
* Removes unnecessary and redundant code (CompareFiles, ImageReader).
* Fixes bug with verification progress updates.
* All .zip files now unzipped before burning.
* All non-.zip files not unzipped before burning.
* Removes unnecessary complexity, e.g. unnecessary scoped_ptrs.

BUG=292956
BUG=337883
BUG=335404

Review URL: https://codereview.chromium.org/149313003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251704 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251704