Create copy of context record before passing it to StackWalk64

Create copy of context record before passing it to StackWalk64

StackWalk64 may modify EXCEPTION_POINTERS struct that is passed
to it from constructor of StackTrace.
In the case of StackDumpExceptionFilter the struct that is passed
to constructor of StackTrace may be later passed to other (chained)
exception filter(s), so it shouldn't be modified.

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269296

[awong, 2014-05-02 19:07:16]

LGTM

[awong, 2014-05-02 19:07:22]

On 2014/05/02 19:07:16, awong wrote:
> LGTM

nice fix.

[marcing, 2014-05-05 15:38:21]

On 2014/05/02 19:07:22, awong wrote:
> On 2014/05/02 19:07:16, awong wrote:
> > LGTM
> 
> nice fix.

Thanks. Can it be committed now or is there anything else I should do?

[awong, 2014-05-07 21:48:00]

Oh sorry. I didn't realize you were waiting on me. Still LGTM.

On 2014/05/05 15:38:21, marcing wrote:
> On 2014/05/02 19:07:22, awong wrote:
> > On 2014/05/02 19:07:16, awong wrote:
> > > LGTM
> > 
> > nice fix.
> 
> Thanks. Can it be committed now or is there anything else I should do?

[marcing, 2014-05-08 10:11:53]

The CQ bit was checked by marcing@opera.com

[commit-bot: I haz the power, 2014-05-08 10:14:17]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/marcing@opera.com/267463003/1

[commit-bot: I haz the power, 2014-05-09 14:54:05]

Change committed as 269296