Have to call renderer->finish() before reading a buffer otherwise you can
get stale data.
Enable IndexBufferOffsetTest.UInt8Index/ES2_VULKAN which now works.
Disable LineLoopTest.LineLoopUShortIndexBuffer/ES2_VULKAN which stopped
working on Windows with Intel GPU.

BUG=angleproject:2659

Change-Id: I1e21b0e1dacd3368923caf18e767e34ab696eef6
Reviewed-on: https://chromium-review.googlesource.com/1227032
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>