Fixing analysis_canvas treatment of save layers with src xfermode

Fixing analysis_canvas treatment of save layers with src xfermode

Code in AnalysisCanvas::willSaveLayer was treating the case of layers
composited with kSrc_Mode as if they did not affect the destination,
when in fact it is kDst_Mode that does not affect the destination.
As a result of this error, the compositor was culling layers that
contained opaque canvas elements, which are composited with
'src' for performance.

BUG=464694
TEST=skia_unittest AnalysisCanvasTest.SaveLayerWithXfermode

Committed: https://crrev.com/9b40df656981fa2e9eaf158f22016b0d566bdaa8
Cr-Commit-Position: refs/heads/master@{#319719}

[Justin Novosad, 2015-03-09 18:38:02]

junov@chromium.org changed reviewers:
+ fmalita@chromium.org, reed@chromium.org

[reed1, 2015-03-09 19:00:11]

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

[reed1, 2015-03-09 19:00:12]

lgtm

[Justin Novosad, 2015-03-09 19:01:10]

The CQ bit was checked by junov@chromium.org

[commit-bot: I haz the power, 2015-03-09 19:02:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/990983003/1

[f(malita), 2015-03-09 19:03:09]

lgtm++

[commit-bot: I haz the power, 2015-03-09 20:14:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-09 20:14:49]

Patchset 1 (id:??) landed as
https://crrev.com/9b40df656981fa2e9eaf158f22016b0d566bdaa8
Cr-Commit-Position: refs/heads/master@{#319719}