Fix memory leak. Make "V8 Linux - memcheck" build bot happy.

Fix memory leak. Make "V8 Linux - memcheck" build bot happy.

Flags::SetFlagsFromCommandLine allocates memory to hold copies of string
arguments when calling Flag::set_string_value(..., true) and presently
noone deallocates this. Resetting the flags will clear this memory.
Since Flags can be used throughout the entire V8 lifetime,
Dispose/Teardown seems like the right location to free this
memory.

This is rarely a problem in practice, but the memcheck buildbot (rightly)
complains.

BUG=
R=machenbach@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=23395

[vogelheim, 2014-08-26 09:29:50]

vogelheim@chromium.org changed reviewers:
+ machenbach@chromium.org

[vogelheim, 2014-08-26 09:31:11]

@machenbach: Can I somehow trigger the 'memcheck' buildbot to verify this
actually resolves the issue?

[Michael Achenbach, 2014-08-26 10:52:22]

On 2014/08/26 09:31:11, vogelheim wrote:
> @machenbach: Can I somehow trigger the 'memcheck' buildbot to verify this
> actually resolves the issue?

LGTM and nope

[vogelheim, 2014-08-26 11:01:07]

Committed patchset #1 manually as 23395 (presubmit successful).