Remove NOTREACHED verifying no previous exceptions are set in PepperTryCatch

Remove NOTREACHED verifying no previous exceptions are set in PepperTryCatch

When setting an exception we check that no other exceptions have been set.
However, sometimes it is preferable not to bail out of the
codepath immediately because the code becomes messier. In particular, if
the context is destroyed, an exception will be set which can happen upon
construction of the try/catch. Keeping this NOTREACHED means that we have to check
for an exception after the construction of every try/catch. I can't see a
problem with not checking the exception immediately - other operations will
fail and the result of the try-catch will eventually be set.

BUG=303491
Committed: https://crrev.com/36ba52d60b693dfe4980b2b73169988f13251324
Cr-Commit-Position: refs/heads/master@{#294046}

[raymes, 2014-09-09 03:35:39]

raymes@chromium.org changed reviewers:
+ dmichael@chromium.org

[dmichael (off chromium), 2014-09-09 20:28:57]

lgtm

[raymes, 2014-09-09 23:22:33]

The CQ bit was checked by raymes@chromium.org

[commit-bot: I haz the power, 2014-09-09 23:25:14]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/raymes@chromium.org/554173002/20001

[commit-bot: I haz the power, 2014-09-10 00:12:38]

Committed patchset #2 (id:20001) as 1dfdcb5fb80c95cf0bf7c51b3dfaa0c8a87e8b84

[commit-bot: I haz the power, 2014-09-10 03:56:50]

Patchset 2 (id:??) landed as
https://crrev.com/36ba52d60b693dfe4980b2b73169988f13251324
Cr-Commit-Position: refs/heads/master@{#294046}