New flingCancel flag to prevent fling boosting.
New flingCancel flag to prevent fling boosting.

This flag is used by Chromium in order to prevent flingCancel
from being used as a part of the fling boost events sequence.
Previously (without this flag), when Chromium called native
cancelFling method, flingCancel event was deferred,
but the proper behaviour should be to cancel fling instantly.

See: https://codereview.chromium.org/792833002/

BUG=440886

Review URL: https://codereview.chromium.org/789223002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@187163 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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