Revert "Fix crash with CVO turned on for VP9 codec"

This reverts commit 29b1a1c0c7c6f4b1ae4d63844b1dfaa7a72530a0.

TBR=guoweis@webrtc.org
BUG=

Review URL: https://webrtc-codereview.appspot.com/48929004

Cr-Commit-Position: refs/heads/master@{#8952}
diff --git a/webrtc/modules/video_coding/main/source/generic_encoder.cc b/webrtc/modules/video_coding/main/source/generic_encoder.cc
index 17ee4d6..0cc2ec4 100644
--- a/webrtc/modules/video_coding/main/source/generic_encoder.cc
+++ b/webrtc/modules/video_coding/main/source/generic_encoder.cc
@@ -8,7 +8,6 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "webrtc/base/checks.h"
 #include "webrtc/engine_configurations.h"
 #include "webrtc/modules/video_coding/main/source/encoded_frame.h"
 #include "webrtc/modules/video_coding/main/source/generic_encoder.h"
@@ -21,7 +20,10 @@
 // Map information from info into rtp. If no relevant information is found
 // in info, rtp is set to NULL.
 void CopyCodecSpecific(const CodecSpecificInfo* info, RTPVideoHeader** rtp) {
-  DCHECK(info);
+  if (!info) {
+    *rtp = NULL;
+    return;
+  }
   switch (info->codecType) {
     case kVideoCodecVP8: {
       (*rtp)->codec = kRtpVideoVp8;
@@ -44,6 +46,8 @@
       (*rtp)->simulcastIdx = info->codecSpecific.generic.simulcast_idx;
       return;
     default:
+      // No codec specific info. Change RTP header pointer to NULL.
+      *rtp = NULL;
       return;
   }
 }