Adjust activity display metrics based on stack configuration.

Apps normally use context.getResources().getDisplayMetrics()
or getWindowManager().getDefaultDisplay() to get information
about the screen dimensions. Not all the screen space is available
for apps in a multi-window environment, so we limit the dimensions
of the display object exposed to the app to that of the containing
stack.

Bug: 19225079
Bug: 19354838
Change-Id: I8dc3a6c9b99ecedcca28fc4ddaba9f31feb4f871