Fix a timing bug in multibuffer.

media/blink/multibuffer_data_source.cc

Index: media/blink/multibuffer_data_source.cc
diff --git a/media/blink/multibuffer_data_source.cc b/media/blink/multibuffer_data_source.cc
index a343fee303aef91f428fcad47dcf86f04ba6b61a..96c6aa28f80b11daa70ef6eadad687927da251d5 100644
--- a/media/blink/multibuffer_data_source.cc
+++ b/media/blink/multibuffer_data_source.cc
@@ -517,10 +517,11 @@ void MultibufferDataSource::ProgressCallback(int64_t begin, int64_t end) {
   if (assume_fully_buffered())
     return;
 
+  base::AutoLock auto_lock(lock_);
+
   if (end > begin) {
     // TODO(scherkus): we shouldn't have to lock to signal host(), see
     // http://crbug.com/113712 for details.
-    base::AutoLock auto_lock(lock_);
     if (stop_signal_received_)
       return;
 
@@ -532,10 +533,13 @@ void MultibufferDataSource::ProgressCallback(int64_t begin, int64_t end) {
 
 void MultibufferDataSource::UpdateLoadingState(bool force_loading) {

[sandersd (OOO until July 31), 2016/09/21 01:13:39]

Nit: Add _Locked suffix?

[hubbe, 2016/09/21 04:19:22]

Done

   DVLOG(1) << __func__;
+  lock_.AssertAcquired();
   if (assume_fully_buffered())
     return;
   // Update loading state.
   bool is_loading = !!reader_ && reader_->IsLoading();
+  if (read_op_)
+    is_loading = true;

[sandersd (OOO until July 31), 2016/09/21 01:13:39]

This means nothing to me, but I'll believe you.

[hubbe, 2016/09/21 04:19:22]

Well, basically we can't destroy reader_ if there is a read operation pending.
There are a few ways to do this:

1) pretend like we're loading if a read operation is pending. This sort of makes
sense as reading will move the read pointer and cause additional buffering.

2) just do "if(read_op_) return", which just prevents us from going to/from a
loading state while a read is pending. Should also work, but just doesn't feel
as correct to me.

3) Do the state to not loading now, but destroy reader_ later. (Seems a bit more
complicated to me, as the state might change again between now and then...)

   if (force_loading || is_loading != loading_) {
     loading_ = is_loading || force_loading;