Implement a high-QP threshold for Android H.264.

Android hardware H.264 seems to keep a steady high-QP flow instead of
dropping frames, so framedrops aren't sufficient to detect a bad state
where downscaling would be beneficial.

BUG=webrtc:4968
R=magjed@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1364253002 .

Cr-Commit-Position: refs/heads/master@{#10078}

webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc

@@ -579,8 +579,11 @@ int VP8EncoderImpl::InitEncode(const VideoCodec* inst,
   }
 
   rps_.Init();
+  // Disable both high-QP limits and framedropping. Both are handled by libvpx
+  // internally.
+  const int kDisabledBadQpThreshold = 64;
   quality_scaler_.Init(codec_.qpMax / QualityScaler::kDefaultLowQpDenominator,
-                       false);
+                       kDisabledBadQpThreshold, false);
   quality_scaler_.ReportFramerate(codec_.maxFramerate);
 
   return InitAndSetControlSettings();