Extend PlatformSpeechSynthesizerMock with an utterance queue.

Clusterfuzz repeatedly runs up against a known limitation of this mock
implementation of PlatformSpeechSynthesizer, that of not being able
to handle the addition of new utterances while one is underway.

Lift the limitation and keep a queue.

R=dmazzoni,haraken
BUG=450142

Review URL: https://codereview.chromium.org/884973003

git-svn-id: svn://svn.chromium.org/blink/trunk@189298 bbb929c8-8fbe-4397-9dbb-9b2b20218538
12 files changed
tree: ea73fa304500b3271bb204bcad952ff7ddf41890
  1. third_party/