Add toWebCoreString() / toWebCoreAtomicString() overloads taking a v8::String

Add toWebCoreString() / toWebCoreAtomicString() overloads taking a v8::String
input since as lot of callers already have a v8::String or already did a
v8::Value::IsString() check. Those callers now use the faster overload instead
of using the one that takes a v8::String as input.

The new overload is faster because it does not use v8StringResource and
thus bypasses useless checks when the input is already a v8::String.

Note that the overload taking a v8::Value as input will eventually
disappear. All callers should either use V8TRYCATCH_FOR_V8STRINGRESOURCE()
macro instead of the v8::String overload depending on the input type.

R=haraken
BUG=

Review URL: https://chromiumcodereview.appspot.com/24139004

git-svn-id: svn://svn.chromium.org/blink/trunk@157828 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert "Switch MutationEvents UseCounter to use countDeprecation."
Revert "Auto-rebaseline for r157796"

This reverts commit 58d5f52f2ddf66c8dac3b9c4fa8ccfe7fb6cdb1f.
This reverts commit 12abf0e5c1a4280b1177b3ea2bf2cb798492dac3.

http://src.chromium.org/viewvc/blink?view=revision&revision=157796

This CL broke Telemetry.  In particular, the ConsoleOutputStream test from telemetry_unittests:
http://build.chromium.org/p/tryserver.chromium/builders/mac_rel/builds/169251/steps/telemetry_unittests/logs/testConsoleOutputStream

It might have also broken Telemetry itself because the perf bots appear hosed
as well.

TBR=ojan

Review URL: https://codereview.chromium.org/23483045

git-svn-id: svn://svn.chromium.org/blink/trunk@157830 bbb929c8-8fbe-4397-9dbb-9b2b20218538