Reintroduce error suppression in DebugTest expectMessage().

- Add error suppression back to expectMessage to prevent potentially
  dirty error state from affecting subsequent checks within a same
  test case. Error suppression was removed in b/18915042 when it was
  errorneously assumed that it was no longer needed after fixing
  b/18915339.
- Tolerate resource leakage in shader_source test.

Bug: 19589360
Bug: 18915042
Change-Id: I4e269f757c99173d4d7f0d5cc273699c0cb69628
2 files changed