Extend the partial_update test to test undefined frame content

This update add two more tests for EGL_KHR_partial_update to
test the following condition:
1. If the program renders outside the damage region, the entire
buffer content is undefined but next frame should be correct.
2. If the program renders before setting damage region, the
entire buffer content is undefined but next frame should be corret.

Change-Id: Ibc49793743f9ae9a9deba5c569983a92854762aa
1 file changed