Copy src in SkDrawLooper::computeFastBounds().

Copy src in SkDrawLooper::computeFastBounds().

We do alias src and dst when building the BBH.  This meant we calculated
the wrong bounds in LayoutTests/ietestcenter/css3/text/textshadow-010.htm.

Not sure how best to test this inside Skia.  It may become moot after I
work through the API changes we were talking about today, but if not I'll
make sure it's tested somehow before I'm done with SkDrawLoopers.

BUG=skia:3186
Committed: https://skia.googlesource.com/skia/+/96a6c4df417a2382dd183b0dbc1c614819795f2a

[mtklein, 2014-12-03 18:57:47]

mtklein@google.com changed reviewers:
+ mtklein@google.com, reed@google.com

[mtklein, 2014-12-03 18:58:04]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-12-03 18:58:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760023004/1

[commit-bot: I haz the power, 2014-12-03 18:58:16]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2014-12-04 00:58 UTC

[reed1, 2014-12-03 18:59:48]

lgtm

[commit-bot: I haz the power, 2014-12-03 19:08:51]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/96a6c4df417a2382dd183b0dbc1c614819795f2a