Ensure that Vector destruction always clears the buffer pointer.

Ensure that Vector destruction always clears the buffer pointer.

This was previously the case, with the exception of inline-buffer Vectors in
"inline storage" mode.

In the process, some code cleanups were performed:
- Removed unused releaseBuffer().
- Added a little LIKELY / UNLIKELY.
- Removed a lot of redundant branches.
- Less work and two removed branches from the destructor path.

Saves 100KB from a GCC-compiled Chrome binary. No real difference on clang,
which seems to inline very differently.


BUG=270545
R=abarth@chromium.org, tsepez@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=157005

[abarth-chromium, 2013-08-30 07:11:10]

lgtm

[Tom Sepez, 2013-08-30 18:05:13]

LGTM2.

[Chris Evans, 2013-08-30 19:11:30]

Committed patchset #1 manually as r157005 (presubmit successful).