Add a null check for the target node in page_click_tracker.

Add a null check for the target node in page_click_tracker.
Events arising from clicks on instance elements in SVG <use> trees may have their
target changed when the instance tree is rebuilt during event processing. In this
case the toNode() call will return NULL for the target.

BUG=171363
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=182049

[csharp, 2013-02-12 14:14:07]

lgtm

[commit-bot: I haz the power, 2013-02-12 15:26:39]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/schenney@chromium.org/12248003/1

[commit-bot: I haz the power, 2013-02-12 15:26:42]

Presubmit check for 12248003-1 failed and returned exit status 1.

INFO:root:Found 1 file(s).

Running presubmit commit checks ...
Running /b/commit-queue/workdir/chromium/PRESUBMIT.py
Running /b/commit-queue/workdir/chromium/chrome/PRESUBMIT.py

** Presubmit ERRORS **
Missing LGTM from an OWNER for files in these directories:
    chrome

[jam, 2013-02-12 17:50:20]

rubberstamp lgtm

[commit-bot: I haz the power, 2013-02-12 18:16:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/schenney@chromium.org/12248003/1

[commit-bot: I haz the power, 2013-02-12 20:34:58]

Retried try job too often on win_rel for step(s) sync_integration_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[Stephen Chennney, 2013-02-12 21:15:24]

On 2013/02/12 20:34:58, I haz the power (commit-bot) wrote:
> Retried try job too often on win_rel for step(s) sync_integration_tests
>
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

Let's try again.

[commit-bot: I haz the power, 2013-02-12 21:16:35]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/schenney@chromium.org/12248003/1

[commit-bot: I haz the power, 2013-02-12 23:03:13]

Change committed as 182049