Bug 1411805 - Update() needs to read some prefs off the main thread. r=gerald

MediaPrefs is our friend.

MozReview-Commit-ID: 3lz5oqUR9R9

--HG--
extra : rebase_source : 31efaf14c29182b00451705b189772aac23acd34
extra : source : 7e9c68fd5fa241fc1d015b352935c2efd0daa1e8

dom/media/MediaCache.cpp

@@ -1306,8 +1306,8 @@ MediaCache::Update()
     }
   }
 
-  int32_t resumeThreshold = Preferences::GetInt("media.cache_resume_threshold", 10);
-  int32_t readaheadLimit = Preferences::GetInt("media.cache_readahead_limit", 30);
+  int32_t resumeThreshold = MediaPrefs::MediaCacheResumeThreshold();
+  int32_t readaheadLimit = MediaPrefs::MediaCacheReadaheadLimit();
 
   for (uint32_t i = 0; i < mStreams.Length(); ++i) {
     actions.AppendElement(StreamAction{});

dom/media/MediaPrefs.h

@@ -94,6 +94,9 @@ private:
                                                               MediaMemoryCachesCombinedLimitPcSysmem, uint32_t, 5);
   DECL_MEDIA_PREF("media.cache.resource-index",               MediaResourceIndexCache, uint32_t, 8192);
 
+  DECL_MEDIA_PREF("media.cache_resume_threshold",             MediaCacheResumeThreshold, int32_t, 10);
+  DECL_MEDIA_PREF("media.cache_readahead_limit",              MediaCacheReadaheadLimit, int32_t, 30);
+
   // AudioSink
   DECL_MEDIA_PREF("accessibility.monoaudio.enable",           MonoAudio, bool, false);
   DECL_MEDIA_PREF("media.resampling.enabled",                 AudioSinkResampling, bool, false);