Clean up renderer fling code.

This cl cleans up the fling handling logic on the renderer side. I've already
added DCHECKs in InputHandlerProxy::HandleGestureFlingStart and some other
functions in input_handler_proxy.cc to make sure that touchscreen and touchpad
flings are not sent to the renderer. Since Mar 28, Autoscroll fling is also
being handled in browser (https://chromium-review.googlesource.com/980965) and
it is safe to delete the dead code from renderer.

To avoid making this cl larger I'll land separate cls for the remaining clean up:
1-Convert fling related layout tests that are using event sender to use gpu
benchmarking or write browser tests instead, delete send GFS/GFC from event sender.
2-DidOvercroll and DidStopFlinging IPCs are not needed anymore.
3-git grep for "fling" and "curve" and check code coverage to remove any remaining
fling related dead code.

Bug: 249063
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ibd1db260c0b3c92c7ccf17156dd38c4865ae1926
Reviewed-on: https://chromium-review.googlesource.com/1117639
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Reviewed-by: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574244}
51 files changed