Fix build issue of missing BackingStrategy vtable.

Fix build issue of missing BackingStrategy vtable.

338ac3d5778afc85b741bafc778d2301eb272bfa added UpdatePictureBufferSize
virtual without being pure or having a definition.

This change marks the method as pure virtual.

BUG=595070
Committed: https://crrev.com/1c8c830c0f2053be82235493b3b96acfb1dbc807
Cr-Commit-Position: refs/heads/master@{#381294}

[avallee, 2016-03-15 18:50:20]

avallee@chromium.org changed reviewers:
+ chcunningham@chromium.org, dalecurtis@chromium.org, jbauman@chromium.org

[avallee, 2016-03-15 18:50:21]

PTAL.

[DaleCurtis, 2016-03-15 18:53:18]

lgtm

[avallee, 2016-03-15 18:54:35]

The CQ bit was checked by avallee@chromium.org

[commit-bot: I haz the power, 2016-03-15 18:54:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1808433003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1808433003/1

[commit-bot: I haz the power, 2016-03-15 19:57:47]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-15 19:59:55]

Description was changed from

==========
Fix build issue of missing BackingStrategy vtable.

338ac3d5778afc85b741bafc778d2301eb272bfa added UpdatePictureBufferSize
virtual without being pure or having a definition.

This change marks the method as pure virtual.

BUG=595070
==========

to

==========
Fix build issue of missing BackingStrategy vtable.

338ac3d5778afc85b741bafc778d2301eb272bfa added UpdatePictureBufferSize
virtual without being pure or having a definition.

This change marks the method as pure virtual.

BUG=595070

Committed: https://crrev.com/1c8c830c0f2053be82235493b3b96acfb1dbc807
Cr-Commit-Position: refs/heads/master@{#381294}
==========

[commit-bot: I haz the power, 2016-03-15 19:59:56]

Patchset 1 (id:??) landed as
https://crrev.com/1c8c830c0f2053be82235493b3b96acfb1dbc807
Cr-Commit-Position: refs/heads/master@{#381294}