Resubmit of refactoring ImageWriterPrivate into the utility process.

I had a few errors in the CL I submitted last week.  I need to resubmit, but to
do that in a new CL I need new approvals (I'm not a committer).  The changes
should be minor.  The first PS is the original CL, the second PS is the changes.

Summary of changes:

* Didn't properly clean up some objects when testing.  In the long run I'd like
to see if I could limit the refcounting some more, but in the mean time I have
to be diligent about cleanup.  Cleanup functions are now automatically added
when the operation is set up for testing.
* When writing we write the whole buffer and not just the part read (due to
Windows alignment requirements). This extra was uninitialized but is now zeroed.
* When validating, if less data was read from the disk than was in the image,
then the image was compared against uninitialized memory.  This was fixed by
failing immediately if fewer bytes are read.

See original CL: https://codereview.chromium.org/61643015/

BUG=345659

TBR=jorgelo@chromium.org
TBR=mpcomplete@chromium.org
TBR=thestig@chromium.org
TBR=jln@chromium.org

Review URL: https://codereview.chromium.org/176103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253773 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253773
Fix a typo in GN build file.

BUG=346597

Review URL: https://codereview.chromium.org/179313002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253774 0039d316-1c4b-4281-b951-d872f2087c98
Fix potential crash in CursorLoaderOzone.

We load a different set of cursors with Ash and DesktopAura. Hence,
we cannot assume kCursorPointer is always loaded. Instead of making
any assumptions for default cursor image, we set this as NULL.

Review URL: https://codereview.chromium.org/179903006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253775 0039d316-1c4b-4281-b951-d872f2087c98
[OSX, rAC] Don't close tooltip bubbles on click.

Tooltip bubbles should stay open when the user clicks on the tooltip
icon.

BUG=325523
R=isherman@chromium.org

Review URL: https://codereview.chromium.org/177043005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253776 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253776