Move string's bits to use bitfields instead of manual masking.
Move string's bits to use bitfields instead of manual masking.

Makes the code more clear and just has less manual management.

Review URL: https://chromiumcodereview.appspot.com/22338002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@155576 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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