Avoid upconverting strings in various places in WebCore
https://bugs.webkit.org/show_bug.cgi?id=118632

Reviewed by Andreas Kling.

Avoid calling String::characters() in various places since it upconverts 8-bit strings to 16-bit strings.

Merge
https://chromium.googlesource.com/chromium/blink/+/a6162e2ad7c7870e22445d3c463d17e7ac871e80
https://chromium.googlesource.com/chromium/blink/+/18095209b3f467758b83894e7b14f813f6953f81
https://chromium.googlesource.com/chromium/blink/+/fefcf2b95d55f24c60fd2e95978cf4544f3c92ca
https://chromium.googlesource.com/chromium/blink/+/8e0527b0fb33998318aedfd74b3511025f7ff294
https://chromium.googlesource.com/chromium/blink/+/feaf798b04597b0849b4000fc305264895d3eac5
https://chromium.googlesource.com/chromium/blink/+/bd1a49103a6e07b1023d2c742d8217769efbffb4

* css/CSSParser.cpp:
(WebCore::CSSParser::setupParser):
(WebCore::CSSParser::parseImageSet):
(WebCore::CSSParser::rewriteSpecifiers):
* css/CSSParserValues.h:
(WebCore::CSSParserString::init):
(WebCore::CSSParserString::clear):
* dom/DatasetDOMStringMap.cpp:
(WebCore::isValidAttributeName):
(WebCore::convertAttributeNameToPropertyName):
(WebCore::propertyNameMatchesAttributeName):
(WebCore::isValidPropertyName):
(WebCore::convertPropertyNameToAttributeName):
* dom/Range.cpp:
(WebCore::Range::toString):
* dom/SecurityContext.cpp:
(WebCore::SecurityContext::parseSandboxPolicy):
* html/canvas/CanvasRenderingContext2D.cpp:
(WebCore::CanvasRenderingContext2D::measureText):
* html/track/TextTrackCue.cpp:
(WebCore::TextTrackCue::markFutureAndPastNodes):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@152611 268f45cc-cd09-0410-ab3c-d52691b4dbfc