Make ASAN happy in MHTMLTest.TestMHTMLEncoding

Make ASAN happy in MHTMLTest.TestMHTMLEncoding

SharedBuffer's valid memory ranges are annotated for ASAN. This means
that the single-argument std::string ctor from char* will read past the
end of the valid range when it scans for a terminating \0.

BUG=none

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197147

[dcheng, 2015-06-12 20:12:38]

dcheng@chromium.org changed reviewers:
+ japhet@chromium.org

[dcheng, 2015-06-12 20:12:39]

Random cleanup.

[Nate Chapin, 2015-06-12 20:14:07]

lgtm

[dcheng, 2015-06-12 20:17:59]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-06-12 20:18:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184863003/1

[commit-bot: I haz the power, 2015-06-13 00:02:38]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-13 00:02:39]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/66497)

[dcheng, 2015-06-15 20:42:44]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-06-15 20:43:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184863003/1

[commit-bot: I haz the power, 2015-06-15 23:43:52]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197147