Avoid ASSERT_NOT_REACHED in blink::floatValueForLength.
Avoid ASSERT_NOT_REACHED in blink::floatValueForLength.

BUG=477786

Review URL: https://codereview.chromium.org/1083083005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@193937 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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