Reland https://codereview.chromium.org/860333002 with fix for test failures.

Reland https://codereview.chromium.org/860333002 with fix for test failures.

Revert "Revert of Make GrScratchKey memory buffer correct size on copy (patchset #1 id:1 of https://codereview.chromium.org/860333002/)"

This reverts commit 988018c817f341c0ce09297b7ba5ba60ba76eba9.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/1c60dfe7ca0db010fa3118a1a2c7ff4c09136ab0

[bsalomon, 2015-01-21 16:58:59]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2015-01-21 16:59:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/863983003/1

[commit-bot: I haz the power, 2015-01-21 17:00:00]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-01-21 22:59 UTC

[brian1, 2015-01-21 17:32:04]

On 2015/01/21 17:00:00, I haz the power (commit-bot) wrote:
> Note for Reviewers:
> The CQ is waiting for an approval.
> If you believe that the CL is not ready yet, or if you would like to L-G-T-M
> with comments then please uncheck the CQ checkbox.
> 
> Waiting for LGTM from valid reviewer(s) till 2015-01-21 22:59 UTC

lgtm

[commit-bot: I haz the power, 2015-01-21 17:32:45]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/1c60dfe7ca0db010fa3118a1a2c7ff4c09136ab0