The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0f728d06389b90c200488eb8a83dfa76d29aaee5

commit 0f728d06389b90c200488eb8a83dfa76d29aaee5
Author: Hongchan Choi <hongchan@chromium.org>
Date: Wed Jul 11 17:07:47 2018

Add UUID for BaseAudioContext

For the future DevTool integration, we need a unique identifier for
each BaseAudioContext. This CL generate a UUID for BaseAudioContext at
its construction time.

Bug:  862411 
Change-Id: I2dda45611af21d57820e1539b22091deb8ddf443
Reviewed-on: https://chromium-review.googlesource.com/1132419
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574204}
[modify] https://crrev.com/0f728d06389b90c200488eb8a83dfa76d29aaee5/third_party/blink/renderer/modules/webaudio/base_audio_context.cc
[modify] https://crrev.com/0f728d06389b90c200488eb8a83dfa76d29aaee5/third_party/blink/renderer/modules/webaudio/base_audio_context.h