Turn on PGO for hwui

This patch is to turn on PGO for hwui. PGO for hwui was turned off for
now because skia, a very important dependency of hwui, was not compiled
with PGO at that time. This patch will be committed along with the patch
to turn on PGO for skia, so that we could get the best performance
improvement.

According to our test, turning on PGO for hwui only introduces an
performance improvement of 5.5%, while with skia PGO turned on, the
improvement increases to 7.6%, both on hwui benchmarks.

Bug: http://b/63768402
Test: None
Change-Id: I17af2cce8e7991aeb89d8bd14ef2e40e6d1049b6