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This allows the scheduler to evolve to a state where it's able to
perform multiple actions of the same type in a given frame. One example
of this is webview where we can stop receiving BeginFrames but still
have to draw any number of times the system asks us to.

BUG=439275

Review URL: https://codereview.chromium.org/1002493006

Cr-Commit-Position: refs/heads/master@{#321625}