Don't hit NOTREACHED for pausing/freezing of OfflineAudioDestinations

Only pause/freeze realtime audio destinations. Offline destinations are
controlled by the thread scheduler itself for pausing/resuming tasks.

BUG=959191

Change-Id: Ie92111af53e651d9d7d3f193921a504935af9c1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1604493Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659275}

third_party/blink/renderer/modules/webaudio/base_audio_context.cc

@@ -185,6 +185,10 @@ void BaseAudioContext::Uninitialize() {
 
 void BaseAudioContext::ContextLifecycleStateChanged(
     mojom::FrameLifecycleState state) {
+  // Don't need to do anything for an offline context.
+  if (!HasRealtimeConstraint())
+    return;
+
   if (state == mojom::FrameLifecycleState::kRunning)
     destination()->GetAudioDestinationHandler().Resume();
   else if (state == mojom::FrameLifecycleState::kFrozen ||