Gallery: Fix a beginning position gap of cropping.

Gallery: Fix a beginning position gap of cropping.

The gap occures when a user moves the mouse cursor fast at the beginning of
cropping. The reason the app uses the first mousemove event's coordinate as the
beginning position of cropping.  The CL uses the mousedown event's coordinate
instead of the first mousemove's one.

BUG=412237
TEST=manually

Committed: https://crrev.com/3b3280d7204d567d4d27c7966782e2d17adcf123
Cr-Commit-Position: refs/heads/master@{#295945}

[hirono, 2014-09-22 08:05:50]

hirono@chromium.org changed reviewers:
+ mtomasz@chromium.org

[hirono, 2014-09-22 08:05:50]

PTAL the CL? Thank you!

[mtomasz, 2014-09-22 09:27:05]

lgtm

[hirono, 2014-09-22 09:29:15]

The CQ bit was checked by hirono@chromium.org

[hirono, 2014-09-22 09:29:23]

On 2014/09/22 09:27:05, mtomasz wrote:
> lgtm

Thanks!

[commit-bot: I haz the power, 2014-09-22 09:30:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/590073002/1

[commit-bot: I haz the power, 2014-09-22 10:01:50]

Committed patchset #1 (id:1) as 097d7cdd79e1a4f369e3c26d3feeca36a5250831

[commit-bot: I haz the power, 2014-09-22 10:02:24]

Patchset 1 (id:??) landed as
https://crrev.com/3b3280d7204d567d4d27c7966782e2d17adcf123
Cr-Commit-Position: refs/heads/master@{#295945}