Make sure temporal layered screenshare frames are sent in at least 2s.

webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h

Index: webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h
diff --git a/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h b/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h
index e11f3d27ef8f3955c33142b89fcc976b02999df5..605f044cde05128572a1770a897293669ca002e5 100644
--- a/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h
+++ b/webrtc/modules/video_coding/codecs/vp8/screenshare_layers.h
@@ -30,6 +30,7 @@ class ScreenshareLayers : public TemporalLayers {
   static const int kTl0Flags;
   static const int kTl1Flags;
   static const int kTl1SyncFlags;
+  static const int kMaxFrameIntervalMs;
 
   ScreenshareLayers(int num_temporal_layers,
                     uint8_t initial_tl0_pic_idx,
@@ -82,7 +83,8 @@ class ScreenshareLayers : public TemporalLayers {
           enhanced_max_qp(-1),
           last_qp(-1),
           debt_bytes_(0),
-          target_rate_kbps_(0) {}
+          target_rate_kbps_(0),
+          last_emitted_timsetamp_(-1) {}
 
     enum class State {
       kNormal,
@@ -95,8 +97,10 @@ class ScreenshareLayers : public TemporalLayers {
     int last_qp;
     uint32_t debt_bytes_;
     uint32_t target_rate_kbps_;
+    int64_t last_emitted_timsetamp_;
 
     void UpdateDebt(int64_t delta_ms);
+    void CheckFrameInterval(int64_t timestamp);
   } layers_[kMaxNumTemporalLayers];
 
   void UpdateHistograms();