Run HTMLSourceTracker hooks only when XSSAuditor is enabled

Run HTMLSourceTracker hooks only when XSSAuditor is enabled

HTMLSourceTracker enables XSSAuditor to examine corresponding raw HTML source
to check if it contains XSS attempts. HTMLSourceTracker is currently very slow
involving full copy of pending input SegmentedString.

Before this CL, HTMLSourceTracker was invoked on every HTMLToken regardless
of XSSAuditor is enabled.

This CL avoids running HTMLSourceTracker when XSSAuditor is not enabled.

BUG=520296
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201530

[kouhei (in TOK), 2015-08-31 23:54:44]

kouhei@chromium.org changed reviewers:
+ yoav@yoav.ws

[Yoav Weiss, 2015-09-01 07:18:03]

On 2015/08/31 23:54:44, kouhei wrote:

LGTM

[kouhei (in TOK), 2015-09-01 07:19:27]

The CQ bit was checked by kouhei@chromium.org

[commit-bot: I haz the power, 2015-09-01 07:19:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1322063002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1322063002/1

[commit-bot: I haz the power, 2015-09-01 07:43:32]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201530