Remove superfluous ThreadLocalTop::catcher field.

Remove superfluous ThreadLocalTop::catcher field.

The external v8::TryCatch handler was computed eagerly and kept in
intact. This changes it to be computed lazily for simplicity and
readability of the code.

R=bmeurer@chromium.org

Committed: https://crrev.com/61e4b6028b094940493b0332c7c107fa18ef2573
Cr-Commit-Position: refs/heads/master@{#27132}

[Benedikt Meurer, 2015-03-11 12:53:05]

Amazing...how many engineering hours went into creating and maintaining this
painful piece of code?

LGTM

[Michael Starzinger, 2015-03-11 12:58:31]

The removal of superfluous will continue until readability improves.

[Michael Starzinger, 2015-03-11 13:34:51]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-03-11 13:35:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/997863003/1

[commit-bot: I haz the power, 2015-03-11 13:36:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-11 13:36:32]

Patchset 1 (id:??) landed as
https://crrev.com/61e4b6028b094940493b0332c7c107fa18ef2573
Cr-Commit-Position: refs/heads/master@{#27132}