Fix frequent recreation of dock divider surface.

The recreation is triggered by content insets changing on every
move, because the content frame used to be full screen. The content
frame should instead be the same as the frame, and content insets
should always be zeroed.

Bug: 24718795

Change-Id: Ia5435d64bfad951885dbcd4200ba6ffc8b7c7ead
1 file changed