Supply separate flags for onBuildTileIndex

Supply separate flags for onBuildTileIndex

This is a follow up to:
https://codereview.chromium.org/1401283003/

Supply separate flags for onBuildTileIndex

Since png and jpeg's implementations of onBuildTileIndex rely on
modifications to their underlying libraries, rather than whether we are
running on Android, use separate flags that can be disabled
independently.

This will allow us to easily turn off the feature. It also is a step
towards building and running on other platforms for testing (e.g.
valgrind/ASAN to find memory leaks etc).

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/fc06e9c0e621744654e231ae6fa4460d88c0e27e

Committed: https://skia.googlesource.com/skia/+/c2d0bc5c20a2a87a49a18c657cd26fe1a23eb874

[msarett, 2015-10-14 21:26:03]

msarett@google.com changed reviewers:
+ scroggo@google.com

[scroggo, 2015-10-14 21:31:08]

LGTM

Thanks!

[msarett, 2015-10-14 21:35:37]

The CQ bit was checked by msarett@google.com

[commit-bot: I haz the power, 2015-10-14 21:35:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1402783008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1402783008/1

[commit-bot: I haz the power, 2015-10-14 21:42:49]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/fc06e9c0e621744654e231ae6fa4460d88c0e27e

[msarett, 2015-10-14 22:20:59]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1394433005/ by msarett@google.com.

The reason for reverting is: Missing an important line..

[msarett, 2015-10-15 12:58:03]

Leon, can you take another look at this?

[scroggo, 2015-10-15 20:08:51]

On 2015/10/15 12:58:03, msarett wrote:
> Leon, can you take another look at this?

Sorry I missed this! LGTM

(You need this because the other instance just defined it for that file, not
this one. We could put it in a header if we wanted to, but I think it's fine as
is.)

[scroggo, 2015-10-15 20:08:55]

The CQ bit was checked by scroggo@google.com

[commit-bot: I haz the power, 2015-10-15 20:09:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1402783008/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1402783008/20001

[commit-bot: I haz the power, 2015-10-15 20:18:08]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/c2d0bc5c20a2a87a49a18c657cd26fe1a23eb874