Reimplement deserialization of SkImageFilter's uniqueID.

Reimplement deserialization of SkImageFilter's uniqueID.

9fa60d ("Simplify flattening to just write enough ... ") simplified just
a tad too much. In particular, it disabled deserialization of
SkImageFilter's uniqueID, which in turn caused the failure of
SkImageFilter's cache, which caused a large regression in Chrome's SVG
filter performance.

The medium-term fix is to switch to the new SkRecordDraw SkPicture
backend, which will make the unique IDs unnecessary.

This change is an "in case of emergecy" CL, in the event that there are
problems switching on the new backend in Chrome. For that reason, it's
minimalist: only the filters used by Chrome are modified, and whitespace
changes are kept to a minimum. In this way, it should be easy to revert
once the new backend goes in.

Committed: https://skia.googlesource.com/skia/+/5e5f948b6b363dbfc8c076d8ff0c6b8e9ea99958

[Stephen White, 2014-08-25 19:01:11]

Here's my backup plan, should problems emerge w/the new
SkPicture backend.

(Just putting it out there.)

[reed1, 2014-08-26 19:12:58]

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

[reed1, 2014-08-26 19:12:58]

lgtm

[Stephen White, 2014-08-26 19:14:37]

The CQ bit was checked by senorblanco@chromium.org

[commit-bot: I haz the power, 2014-08-26 19:15:43]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/senorblanco@chromium.org/503833002/1

[commit-bot: I haz the power, 2014-08-26 19:27:17]

Committed patchset #1 (1) as 5e5f948b6b363dbfc8c076d8ff0c6b8e9ea99958