tree 9330740351e96cdc5b6e2569a5ede5f7c8764a55
parent 8417a7b5140bf6dd27702331e787887a7b8c2e3d
author Tony Wickham <twickham@google.com> 1526519738 -0700
committer Tony <twickham@google.com> 1527012301 -0700

Cleanup how we set back button alpha

Add BackButtonAlphaHandler to set back button alpha, instead of setting
it from multiple places.

Also force back button alpha to be 1 if swipe up is disabled (b/80091187)

Change-Id: I49b63a0e6b033a3a947a847669a398f1b9ff0564