[Cast] Cleanup VideoSender: Dead code removal, lotsa documentation, use uint32 for frame_ids.

This is some prerequisite work to be done before turning VideoSender
into an all-purpose FrameSender, to be used for both audio and video
sending.

1. Removed "frame skip" tracking that wasn't being consumed by anything.
2. Replaced use of int with uint32 for frame IDs, to be consistent with
   the rest of media/cast.  In addition, the logic that used these
   members was simplified/clarified, but behaviorally unchanged.
3. Heavily documented the VideoSender class, methods, and data members.
3. Fixed a bug where ACKs received out-of-order would cause VideoSender
   to re-send frames the receiver doesn't need.

BUG=380023

Review URL: https://codereview.chromium.org/316773003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274998 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 3 deletions

diff --git a/media/cast/cast_defines.h b/media/cast/cast_defines.h
index afb50e0..bf6df39 100644
--- a/media/cast/cast_defines.h
+++ b/media/cast/cast_defines.h
@@ -22,11 +22,13 @@ namespace cast {
 const int64 kDontShowTimeoutMs = 33;
 const float kDefaultCongestionControlBackOff = 0.875f;
 const uint32 kVideoFrequency = 90000;
-const int64 kSkippedFramesCheckPeriodkMs = 10000;
 const uint32 kStartFrameId = UINT32_C(0xffffffff);
 
-// Number of skipped frames threshold in fps (as configured) per period above.
-const int kSkippedFramesThreshold = 3;
+// This is an important system-wide constant.  This limits how much history the
+// implementation must retain in order to process the acknowledgements of past
+// frames.
+const int kMaxUnackedFrames = 255;
+
 const size_t kMaxIpPacketSize = 1500;
 const int kStartRttMs = 20;
 const int64 kCastMessageUpdateIntervalMs = 33;