Make SHA1 computation thread-safe.
Make SHA1 computation thread-safe.

Previously SHA1Transform() kept a static buffer. As result SHA1 was not
always computed correctly when running that code in parallel on multiple
threads. That was causing spurious messages about invalid Message
Integrity attribute when running some tests in chromoting.

R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/57379004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9238}

TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc