use SkMaskCache inside SkBlurMaskFilter

depends on https://codereview.chromium.org/670063004/

BUG=skia:

Review URL: https://codereview.chromium.org/669993003
Revert of create shaderproc for nofilter-opaque-dx (patchset #7 id:120001 of https://codereview.chromium.org/664783004/)

Reason for revert:
Many GMs fixed.  Needs rebaseline, perhaps layout test rebaselines.

Original issue's description:
> create shaderproc for nofilter-opaque-dx
>
>
> speedup nofilter
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/a40a276bcee2246439dcf816273c1307f5c3c69f

TBR=djsollen@google.com,reed@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/656913005
add float equivalent in dumpHex output as comment

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

Review URL: https://codereview.chromium.org/676803002
Add utils to better quantize grayscale values to three bit indices while
compressing coverage masks.

Signed-off-by: Pavel Krajcevski <pavel@cs.unc.edu>

BUG=skia:

Review URL: https://codereview.chromium.org/669243003
Rebaselines for tests affected by image filter PDF change.

(aka https://codereview.chromium.org/644323006/)

TBR=mtklein@google.com
NOTRY=true

BUG=skia:

Review URL: https://codereview.chromium.org/671303003
Adding an option to render only the shadow in SkDropShadowImageFilter

This is basically how blink uses the filter. Currently, I can't use it for "ShadowOnly" mode with the filter at all, but instead of copying the code and risking to have the codepaths diverge, I'm simply going to add the option here.

BUG=skia:

Review URL: https://codereview.chromium.org/646213004
Remove test expectations from ignored-tests.txt.

TBR=mtklein@google.com
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/659393006
Don't use MIP filter mode on compressed textures

Add compressed texture image downsample GMs

BUG=chromium:426331

Review URL: https://codereview.chromium.org/672863003