Revert of Revert of Add test_runner hook to dump drag image.

Revert of Revert of Add test_runner hook to dump drag image. (patchset #1 id:1 of https://codereview.chromium.org/925743002/)

Reason for revert:
Reverting this breaks the blink side CL that depended on the new test_runner hook: https://codereview.chromium.org/886323005/
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux/builds/44149

Fix is here:
https://codereview.chromium.org/918313003/
I think it was failing CQ for unrelated reasons, so reverting this.

Original issue's description:
> Revert of Add test_runner hook to dump drag image. (patchset #3 id:40001 of https://codereview.chromium.org/904833004/)
> 
> Reason for revert:
> Caused pixel test flakiness.
> 
> Original issue's description:
> > Add test_runner hook to dump drag image.
> >
> > This is used by:
> > https://codereview.chromium.org/886323005/
> >
> > BUG=451759
> >
> > Committed: https://crrev.com/3726d659908604350bc03ef02d1ccc5cdc097dd5
> > Cr-Commit-Position: refs/heads/master@{#315915}
> 
> TBR=junov@chromium.org,jackhou@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=451759
> 
> Committed: https://crrev.com/29881876aff6c4639ac9378a2911be87b73c8a0a
> Cr-Commit-Position: refs/heads/master@{#316136}

BUG=451759, 458077

[jackhou1, 2015-02-13 03:03:48]

Created Revert of Revert of Add test_runner hook to dump drag image.

[tkent, 2015-02-13 03:07:03]

Not lgtm.

We already reverted, and I'll add fast/images/drag-image.html to
TestExpectations.
It's important to make existing tests stable.

[jackhou1, 2015-02-13 03:23:14]

On 2015/02/13 03:07:03, tkent wrote:
> Not lgtm.
> 
> We already reverted, and I'll add fast/images/drag-image.html to
> TestExpectations.
> It's important to make existing tests stable.

Ah I'd forgotten about TestExpectations. Thanks for sorting that out
(http://crrev.com/920853003).

I've removed the TBR, NOTRY etc from this CL. Along with the Patch Set 2, it
should be everything that's needed to fix the test. Could you review it again?

If you prefer, I can instead put together a new CL, or reopen the previous one
(http://crrev.com/886323005).

[tkent, 2015-02-13 03:39:18]

On 2015/02/13 03:23:14, jackhou1 wrote:
> I've removed the TBR, NOTRY etc from this CL. Along with the Patch Set 2, it
> should be everything that's needed to fix the test. Could you review it again?

The CL looks a revert, and it's very confusing.

> If you prefer, I can instead put together a new CL, or reopen the previous one
> (http://crrev.com/886323005).

I prefer this way.  Either of new CL or uploading new Patch Set to the original
CL is ok.

[jackhou1, 2015-02-13 04:53:32]

On 2015/02/13 03:39:18, tkent wrote:
> On 2015/02/13 03:23:14, jackhou1 wrote:
> > I've removed the TBR, NOTRY etc from this CL. Along with the Patch Set 2, it
> > should be everything that's needed to fix the test. Could you review it
again?
> 
> The CL looks a revert, and it's very confusing.
> 
> > If you prefer, I can instead put together a new CL, or reopen the previous
one
> > (http://crrev.com/886323005).
> 
> I prefer this way.  Either of new CL or uploading new Patch Set to the
original
> CL is ok.

New CL is here: https://codereview.chromium.org/916893003/