[multibuffer] Always clear cancel_upon_defer_ when playback starts.

During the changes made for preload=metadata suspend, it was assumed
that OnBufferingHaveEnough() had no lingering effects after the next
call to MediaIsPlaying(). It turns out this was not true. The method
would only clear |cancel_upon_defer_| the first time.

The fix is to always clear |cancel_upon_defer_| once the DataSource
has been informed of playback. A new unittest verifies this.

BUG=1004530
TEST=new unittest, clip from bug does not create more than 1 loader
after a seek from the suspended state.

R=tguilbert

Change-Id: I7655d7ff0ee0ba1024ec0486331d84aeda16918c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807160
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697421}

media/blink/multibuffer_data_source.cc

@@ -304,11 +304,16 @@ void MultibufferDataSource::MediaPlaybackRateChanged(double playback_rate) {
 
 void MultibufferDataSource::MediaIsPlaying() {
   DCHECK(render_task_runner_->BelongsToCurrentThread());
+
+  // Always clear this since it can be set by OnBufferingHaveEnough() calls at
+  // any point in time.
+  cancel_on_defer_ = false;
+
   if (media_has_played_)
     return;
 
   media_has_played_ = true;
-  cancel_on_defer_ = false;
+
   // Once we start playing, we need preloading.
   preload_ = AUTO;
   UpdateBufferSizes();

media/blink/multibuffer_data_source_unittest.cc

@@ -1305,6 +1305,7 @@ TEST_F(MultibufferDataSourceTest,
 
   // Marking the media as playing should prevent deferral. It also tells the
   // data source to start buffering beyond the initial load.
+  EXPECT_FALSE(data_source_->cancel_on_defer_for_testing());
   data_source_->MediaIsPlaying();
   data_source_->OnBufferingHaveEnough(false);
   CheckCapacityDefer();
@@ -1316,6 +1317,7 @@ TEST_F(MultibufferDataSourceTest,
   ReceiveData(kDataSize);
   ASSERT_TRUE(active_loader());
   data_source_->OnBufferingHaveEnough(true);
+  EXPECT_TRUE(data_source_->cancel_on_defer_for_testing());
   ASSERT_TRUE(active_loader());
   ASSERT_FALSE(data_provider()->deferred());
 
@@ -1329,6 +1331,26 @@ TEST_F(MultibufferDataSourceTest,
   EXPECT_GT(bytes_received, 0);
   EXPECT_LT(bytes_received + kDataSize, kFileSize);
   EXPECT_FALSE(active_loader_allownull());
+
+  // Verify playback resumes correctly too.
+  data_source_->MediaIsPlaying();
+  EXPECT_FALSE(data_source_->cancel_on_defer_for_testing());
+
+  // A read from a previously buffered range won't create a new loader yet.
+  EXPECT_CALL(*this, ReadCallback(kDataSize));
+  ReadAt(kDataSize);
+  EXPECT_FALSE(active_loader_allownull());
+
+  // Reads from an unbuffered range will though...
+  EXPECT_CALL(*this, ReadCallback(kDataSize));
+  ReadAt(kFarReadPosition);
+
+  // Receive enough data to exhaust current capacity which would destroy the
+  // loader upon deferral if the flag hasn't been cleared properly.
+  for (int i = 0; i <= (preload_high() / kDataSize) + 1; ++i) {
+    ReceiveData(kDataSize);
+    ASSERT_TRUE(active_loader());
+  }
 }
 
 TEST_F(MultibufferDataSourceTest, SeekPastEOF) {