Bug 1401471. P4 - always access mChannelOffset within the cache monitor. r=gerald

MozReview-Commit-ID: KIQU3PrBUj1

--HG--
extra : rebase_source : 5b012b8ace153124a1f2f158efeaad9057927dd4
extra : intermediate-source : d5219d074f525e614164e7c3076a9df695c55e6c
extra : source : 8f07a48d4ac13162add83cce8677322e148d6f74

dom/media/MediaCache.cpp

@@ -462,7 +462,6 @@ MediaCacheStream::MediaCacheStream(ChannelMediaResource* aClient,
   , mIsTransportSeekable(false)
   , mCacheSuspended(false)
   , mChannelEnded(false)
-  , mChannelOffset(0)
   , mStreamLength(-1)
   , mStreamOffset(0)
   , mPlaybackBytesPerSecond(10000)
@@ -2206,7 +2205,7 @@ MediaCacheStream::GetLength()
 int64_t
 MediaCacheStream::GetOffset() const
 {
-  MOZ_ASSERT(NS_IsMainThread());
+  ReentrantMonitorAutoEnter mon(mMediaCache->GetReentrantMonitor());
   return mChannelOffset;
 }
 

dom/media/MediaCache.h

@@ -460,8 +460,6 @@ private:
   bool mCacheSuspended;
   // True if the channel ended and we haven't seeked it again.
   bool mChannelEnded;
-  // The offset where the next data from the channel will arrive
-  int64_t      mChannelOffset;
   // The reported or discovered length of the data, or -1 if nothing is
   // known
   int64_t      mStreamLength;
@@ -469,6 +467,8 @@ private:
   // The following fields are protected by the cache's monitor can can be written
   // by any thread.
 
+  // The offset where the next data from the channel will arrive
+  int64_t mChannelOffset = 0;
   // The offset where the reader is positioned in the stream
   int64_t           mStreamOffset;
   // For each block in the stream data, maps to the cache entry for the