Simplify DOMTokenList::validateToken() code
Simplify DOMTokenList::validateToken() code

Simplify DOMTokenList::validateToken() code by calling WTFString::find()
instead of manually iterating through the String to find HTML spaces.

R=rob.buis@samsung.com

Review URL: https://codereview.chromium.org/479243002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@180486 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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