A simple replacement for the way passthrough was previously implemented.
Added a state for two fingers passing through as one (e.g. scrolling).
Added a state for all fingers passing though, which is activated after a third finger is placed and lasts until all fingers are released.
TEST= TouchExplorationTest.TwoToOneFingerReleaseSecond, TouchExplorationTest.TwoToOneFingerReleaseFirst, TouchExplorationTest.Passthrough
BUG= 388520
Review URL: https://codereview.chromium.org/
333663006
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@280653 0039d316-1c4b-4281-b951-d872f2087c98