Update frame metrics / viewport when orientation changes

Sending zoom contraints update from TabChildHelper is delayed
until new target viewport size is calculated. The new target
viewport size is used for calculating minimum viewport size.

In addition, AsyncPanZoomController needs to reset also displayPort
when composition bounds have changed.

Conflicts:
	gfx/layers/ipc/AsyncPanZoomController.cpp
Add more framemetrics logging for AsyncPanZoomController

Adapted from embedlite branch
Merge pull request #49 from rainemak/embedlite_26

Update frame metrics / viewport when orientation changes