Detect discarded SkPictureShader pixel refs.

This doesn't address the more general problem, but reduces the race
window significantly.

BUG=440282
R=reed@google.com

Review URL: https://codereview.chromium.org/787043006
Remove MULTILINE, ^, and $ from re finding actual_results.json.

MULTILINE, ^, and $ work based on the platform, but the files being
parsed are from other platforms. As a result, the current code for
extracting the actual_results.json version will not find it in
logfiles produced on Windows when run on Mac.

The code for extracting the exact actual_results.json file to use
from a logfile is itself something of a hack, as this information
should be provided ina more structured manner. This proposed
method of finding the exact file is no worse than the old one, and
in cases like above, better.

Review URL: https://codereview.chromium.org/789253002
More rebaselines.

TBR=bsalomon
BUG=skia:

Review URL: https://codereview.chromium.org/790263002
Rebaseline imagefiltersscaled images (and rm from ignored-tests file)

Rebaselines for https://codereview.chromium.org/785893004/ (Fix MatrixImageFilter computeFastBounds)

TBR=scroggo@google.com

Review URL: https://codereview.chromium.org/794673004
fix for valgrind uninit variables

TBR=bsalomon@google.com
BUG=skia:

Review URL: https://codereview.chromium.org/793773002
Fix to set correct output type when blending when we've read dst

BUG=skia:

Review URL: https://codereview.chromium.org/791143002
Don't store an SkMatrix in BitmapShaderKey.

SkMatrix makes for a poor key component due to mutable/cache fields.

Use its canonical scalars instead.

R=reed@google.com,mtklein@google.com

Review URL: https://codereview.chromium.org/792123002