Cherry pick: VP8: For high overshoot, force drop frame and max-out QP.

source/libvpx/vpx/vp8cx.h

 /*
  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 #ifndef VPX_VP8CX_H_
@@ skipping 309 matching lines @@
    * layer id for each frame to be encoded. Note that this control must be set
    * for every frame prior to encoding. The usage of this control function
    * supersedes the internal temporal pattern counter, which is now deprecated.
    *
    * Supported in codecs: VP8
    */
   VP8E_SET_TEMPORAL_LAYER_ID,
 
   /*!\brief Codec control function to set encoder screen content mode.
    *
+   * 0: off, 1: On, 2: On with more aggressive rate control.
+   *
    * Supported in codecs: VP8
    */
   VP8E_SET_SCREEN_CONTENT_MODE,
 
   /*!\brief Codec control function to set lossless encoding mode.
    *
    * VP9 can operate in lossless encoding mode, in which the bitstream
    * produced will be able to decode and reconstruct a perfect copy of
    * input source. This control function provides a mean to switch encoder
    * into lossless coding mode(1) or normal coding mode(0) that may be lossy.
@@ skipping 358 matching lines @@
 
 VPX_CTRL_USE_TYPE(VP9E_SET_COLOR_SPACE, int)
 
 VPX_CTRL_USE_TYPE(VP9E_GET_ACTIVEMAP, vpx_active_map_t *)
 /*! @} - end defgroup vp8_encoder */
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // VPX_VP8CX_H_