Introduced logic to control the bubble bar stash handle alpha based on
the notification shade state.
Test: TransientBubbleStashControllerTest
Test: Manual. Have bubbles and the bubble bar stashed. Open the
notification shade, observe that the stash handle fades away. Close the
notification shade, observe that the stash handle fades back in.
Have few bubbles, open bubbles test app, click on bubble icon. Observe
the bubble bar expands without blinking.
Test: Manual.
http://recall/-/gx8ASgewUeUS3QYohfrd1J/e1iUtwaFdezKOb0gBRff7Z
Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 376140839
Fixes: 376141264
Change-Id: Id9c473f9aead0e4c5830793d9f3b0b1ae86453e7
mpodolian
f1186f9d14