Revert "Remove children of title node before updating"

It causes performance problems. See
https://code.google.com/p/chromium/issues/detail?id=331076

Micro-benchmarks like http://jsperf.com/setting-document-title regress
about one magnitude.

We need to figure out whether the spec should change or if the CL
could be written in a less performance-intrusive way, or if it's a
performance penalty we accept. So revert for now.

The follow-up "Inhibit title updates when removing children before
setting new value" is reverted too since it has no value without the
first patch.

Reverted CLs:

https://codereview.chromium.org/128603002
https://codereview.chromium.org/107513013

BUG=331076

Review URL: https://codereview.chromium.org/138213005

git-svn-id: svn://svn.chromium.org/blink/trunk@165117 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove dead code from DocumentOrderedMap

Remove dead code from DocumentOrderedMap:
- clear() method is never used
- checkConsistency() is declared but unimplemented
- "wtf/HashCountedSet.h" include is no longer needed

R=esprehn, adamk

Review URL: https://codereview.chromium.org/138573003

git-svn-id: svn://svn.chromium.org/blink/trunk@165118 bbb929c8-8fbe-4397-9dbb-9b2b20218538