SkGIFMovie: Fix corrupted background color

SkGIFMovie: Fix corrupted background color

The 'paintingColor' in onGetBitmap() was used to save the entire
gif's background color while filling the 1st frame of a gif image,
since it is 'static' qualified, so when re-entering this function
for subsequent frames, this saved value will be used directly without
re-obtaining it.
But if asynchronous playing multi gif files in single process without
being controlled, this 'static' will make the 'paintingColor'
corrupted, because the different SkGIFMovie instances hold the same
reference of 'paintingColor'.

Signed-off-by: Lu Tong <lu.x.tong@sonymobile.com>;

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/b5b50a07abb454abaf6ab46db20c6db6f5ecf9f6

[Taka, 2015-06-15 09:20:55]

takahiro.aizawa@sonymobile.com changed reviewers:
+ mtklein@google.com, scroggo@google.com

[mtklein, 2015-06-15 09:47:31]

The CQ bit was checked by mtklein@google.com

[mtklein, 2015-06-15 09:47:32]

lgtm

[commit-bot: I haz the power, 2015-06-15 09:47:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184083002/40001

[commit-bot: I haz the power, 2015-06-15 09:52:49]

Committed patchset #3 (id:40001) as
https://skia.googlesource.com/skia/+/b5b50a07abb454abaf6ab46db20c6db6f5ecf9f6