Make parseCompositeAndBlendOperator() take care of "normal".
Make parseCompositeAndBlendOperator() take care of "normal".

Currently, parseCompositeAndBlendOperator() doesn't recognize "normal".
Fortunately, there are not bugs because all clients set blend mode to "normal"
if this function fails.

BUG=425656

Review URL: https://codereview.chromium.org/671713006

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@184239 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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