Check the validity of cache_ weak ptr in DoFinishHeaders

Speculative fix for 734357
There is just one instance of this crash and the report does not tell much about
whether its an invalid memory access. I am speculating that may be we need to check
if cache_ weak pointer is still valid before invoking a function on it in 
DoFinishHeaders. Will keep a watch if there are more such crashes reported with more information.

BUG=734357
Review-Url: https://codereview.chromium.org/2946633002
Cr-Commit-Position: refs/heads/master@{#480845}
Committed: https://chromium.googlesource.com/chromium/src/+/61ec4c2e31c1d1f9dae24a416b0f5b50157f71d9

[shivanisha, 2017-06-18 00:27:03]

The CQ bit was checked by shivanisha@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-06-18 00:27:08]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[shivanisha, 2017-06-18 00:28:51]

Description was changed from

==========
Speculative fix for 734357
check for cache_ being valid in DoFinishHeaders

BUG=734357
==========

to

==========
Speculative fix for 734357
There is just one instance of this crash and the report does not tell much. I am
speculating that may be we need to check if cache_ weak pointer is still valid 
before invoking a function on it in DoFinishHeaders.

BUG=734357
==========

[shivanisha, 2017-06-18 00:28:52]

shivanisha@chromium.org changed reviewers:
+ mmenke@chromium.org

[shivanisha, 2017-06-18 00:33:16]

Description was changed from

==========
Speculative fix for 734357
There is just one instance of this crash and the report does not tell much. I am
speculating that may be we need to check if cache_ weak pointer is still valid 
before invoking a function on it in DoFinishHeaders.

BUG=734357
==========

to

==========
Speculative fix for 734357
There is just one instance of this crash and the report does not tell much about
whether its an invalid memory access. I am speculating that may be we need to
check
if cache_ weak pointer is still valid before invoking a function on it in 
DoFinishHeaders. Will keep a watch if there are more such crashes reported with
more information.

BUG=734357
==========

[shivanisha, 2017-06-18 00:34:58]

mmenke@, PTAL, Thanks!

[commit-bot: I haz the power, 2017-06-18 01:48:41]

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

[commit-bot: I haz the power, 2017-06-18 01:48:42]

Dry run: This issue passed the CQ dry run.

[mmenke, 2017-06-19 17:46:45]

On 2017/06/18 00:34:58, shivanisha wrote:
> mmenke@, PTAL, Thanks!

LGTM

[shivanisha, 2017-06-20 14:47:37]

The CQ bit was checked by shivanisha@chromium.org

[commit-bot: I haz the power, 2017-06-20 14:47:55]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-06-20 16:21:14]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1497970057470470, "parent_rev":
"9ce0a3b055104bd88dda0412d766a22f8423b378", "commit_rev":
"61ec4c2e31c1d1f9dae24a416b0f5b50157f71d9"}

[commit-bot: I haz the power, 2017-06-20 16:21:28]

Description was changed from

==========
Speculative fix for 734357
There is just one instance of this crash and the report does not tell much about
whether its an invalid memory access. I am speculating that may be we need to
check
if cache_ weak pointer is still valid before invoking a function on it in 
DoFinishHeaders. Will keep a watch if there are more such crashes reported with
more information.

BUG=734357
==========

to

==========
Speculative fix for 734357
There is just one instance of this crash and the report does not tell much about
whether its an invalid memory access. I am speculating that may be we need to
check
if cache_ weak pointer is still valid before invoking a function on it in 
DoFinishHeaders. Will keep a watch if there are more such crashes reported with
more information.

BUG=734357

Review-Url: https://codereview.chromium.org/2946633002
Cr-Commit-Position: refs/heads/master@{#480845}
Committed:
https://chromium.googlesource.com/chromium/src/+/61ec4c2e31c1d1f9dae24a416b0f...
==========

[commit-bot: I haz the power, 2017-06-20 16:21:30]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/61ec4c2e31c1d1f9dae24a416b0f...