Fix crash on BLU Life Play devices related to switch preferences.

Fix crash on BLU Life Play devices related to switch preferences.

ChromeSwitchPreference uses setWidgetLayoutResource() to show a Material
switch, but on BLU Life Play devices, this has no effect and the default
switch is shown instead. As a result ChromeSwitchPreference.onBindView()
couldn't find the Material switch and was crashing with a NPE. This
fixes the crash by adding a null check, though these devices will still
show a non-material switch.

BUG=451447
R=dtrainor@chromium.org

[newt (away), 2015-02-02 23:56:58]

newt@chromium.org changed reviewers:
+ dtrainor@chromium.org

[newt (away), 2015-02-02 23:57:03]

On 2015/02/02 23:56:58, newt wrote:

PTAL

[David Trainor- moved to gerrit, 2015-02-03 00:16:18]

lgtm

[newt (away), 2015-02-03 00:29:25]

The CQ bit was checked by newt@chromium.org

[commit-bot: I haz the power, 2015-02-03 00:31:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/894873004/1

[commit-bot: I haz the power, 2015-02-03 02:32:48]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-02-03 02:32:50]

Try jobs failed on following builders:
  win8_chromium_rel on tryserver.chromium.win (None)

[commit-bot: I haz the power, 2015-02-03 02:41:29]

Patchset 1 (id:??) landed as
https://crrev.com/796a0bc0a3064f17357460187a02d7b216853e0d
Cr-Commit-Position: refs/heads/master@{#314250}

[newt (away), 2015-02-03 02:41:33]

Committed patchset #1 (id:1) to pending queue manually as
361ff6c4c5d5fe27bf415eafbfe5cb849bc66712 (presubmit successful).