There were various booleans on `ReflowResults` that represented various
actions that might have been taken during a reflow request. Replace
those with a bitflags that better represents what reflow phases have
actually been run. Update variable names to reflect what they mean.
In addition, run some post-layout tasks unconditionally. They are
already contingent on the results returned from layout.
This simplifies and clarifies the code a good deal.
Testing: This should not change observable behavior and thus is covered
by existing WPT tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
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