Make StyleSheetInsert a more realistic perf test.

This was testing inserting stylesheets in a page with no style
recalc. Instead, force a recalc before and after the stylesheet
inserts to make it better match what a real page would look like.

BUG=323732

Review URL: https://codereview.chromium.org/92203002

git-svn-id: svn://svn.chromium.org/blink/trunk@162788 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Have CSSFontFeatureValue store the tag as an AtomicString instead of a String

Have CSSFontFeatureValue store the tag as an AtomicString instead of a String.
CSSFontFeatureValue objects are constructed in:
- CSSParser::parseFontFeatureTag() where the tag is a CSSParserString that can
be easily be used to construct either a String or an AtomicString
- CSSComputedStyleDeclaration::getPropertyCSSValue() where it is constructed
from a FontFeature. FontFeature stores the tag as an AtomicString.

CSSFontFeatureValue::tag() getter is used by:
- FontBuilder::setFeatureSettingsValue() to construct a FontFeature object,
which requires the tag as a AtomicString and thus required us to convert
the tag from String to AtomicString.
- CSSFontFeatureValue::customCSSText() which uses StringBuilder::append(), so
it does not matter if the tag is a String or AtomicString.
- CSSFontFeatureValue::equals() for comparing the tags of 2 CSSFontFeatureValue
objects. In this case, keeping the tag as AtomicString would be more efficient.

Therefore, by having CSSFontFeatureValue store the tag as an AtomicString, we
gain consistency with FontFeature, which is important as we need 2-way conversion
from CSSFontFeatureValue <-> FontFeature. Also, it makes
CSSFontFeatureValue::equals() faster.

R=eseidel
BUG=323739

Review URL: https://codereview.chromium.org/92493003

git-svn-id: svn://svn.chromium.org/blink/trunk@162789 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark http/tests/media/media-source/webkitmediasource-removesourcebuffer-texttrack.html as crashy

BUG=324120
TBR=
NOTRY=true

Review URL: https://codereview.chromium.org/93243002

git-svn-id: svn://svn.chromium.org/blink/trunk@162790 bbb929c8-8fbe-4397-9dbb-9b2b20218538