fix canplaythrough

media/blink/buffered_data_source_host_impl.h

Index: media/blink/buffered_data_source_host_impl.h
diff --git a/media/blink/buffered_data_source_host_impl.h b/media/blink/buffered_data_source_host_impl.h
index 7dc39ea331a6ab447e0998e6ca19ce10e254acdf..2caa4098fd6148aa02fb66092d7314f462a7d4de 100644
--- a/media/blink/buffered_data_source_host_impl.h
+++ b/media/blink/buffered_data_source_host_impl.h
@@ -6,7 +6,9 @@
 #define MEDIA_BLINK_BUFFERED_DATA_SOURCE_HOST_IMPL_H_
 
 #include <stdint.h>
+#include <deque>
 
+#include "base/callback.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "media/base/ranges.h"
@@ -35,7 +37,7 @@ class MEDIA_BLINK_EXPORT BufferedDataSourceHost {
 class MEDIA_BLINK_EXPORT BufferedDataSourceHostImpl
     : public BufferedDataSourceHost {
  public:
-  BufferedDataSourceHostImpl();
+  explicit BufferedDataSourceHostImpl(const base::Closure& progress_cb);
   ~BufferedDataSourceHostImpl() override;
 
   // BufferedDataSourceHost implementation.
@@ -50,7 +52,20 @@ class MEDIA_BLINK_EXPORT BufferedDataSourceHostImpl
 
   bool DidLoadingProgress();
 
+  // Returns true if we have enough buffered bytes to play from now
+  // until the end of media
+  bool CanPlayThrough(base::TimeDelta current_position,
+                      base::TimeDelta media_duration,
+                      double playback_rate) const;
+
  private:
+  // Returns number of bytes not yet loaded in the given interval.
+  int64_t UnloadedBytesInInterval(const Interval<int64_t>& interval) const;
+
+  // Returns an estimate of the download rate.
+  // Returns 0.0 if an estimate cannot be made.
+  double DownloadRate() const;
+
   // Total size of the data source.
   int64_t total_bytes_;
 
@@ -62,6 +77,11 @@ class MEDIA_BLINK_EXPORT BufferedDataSourceHostImpl
   // DidLoadingProgress().
   bool did_loading_progress_;
 
+  // Contains how much we had downloaded at a given time.
+  // Pruned to contain roughly the last 10 seconds of data.
+  std::deque<std::pair<base::TimeTicks, uint64_t>> download_history_;

[sandersd (OOO until July 31), 2017/04/25 22:00:57]

I'm a bit worried about the size and complexity of this deque. I think it should
be abstracted into its own class, and I would propose implementing it using a
fixed number of tagged bins instead.

Specifically, something like this: struct { int64_t time; int64_t bytes; }
bins[10];

(This example structure support second-granularity tracking over ten seconds in
a fixed amount of memory; each transfer just gets counted into bin[now % 10].)

[hubbe, 2017/04/25 23:47:03]

Given that each entry represents at least 1000 bytes, the overhead seems pretty
small. I didn't have a lot of luck with reducing the complexity, and I don't
think doing the modular math myself is simpler than letting deque do it for me.

As for breaking it out: I could, but personally I don't think it's worth it.
Dale, what do you think?

[DaleCurtis, 2017/04/26 00:11:26]

What does the size of this look like currently? I don't think this class does
much so I'm happy to have it in here so long as it's well tested. I share Dan's
concerns about the growth of it though, so having an idea of what it looks like
after 15 minutes of playback would be interesting.

[hubbe, 2017/04/26 00:24:27]

There is a maximum of 1000 entries right now.

+  base::Closure progress_cb_;
+
   DISALLOW_COPY_AND_ASSIGN(BufferedDataSourceHostImpl);
 };