VTVDA: Verify |picture_id| in ResusePictureBuffer().

media/gpu/vt_video_decode_accelerator_mac.cc

Index: media/gpu/vt_video_decode_accelerator_mac.cc
diff --git a/media/gpu/vt_video_decode_accelerator_mac.cc b/media/gpu/vt_video_decode_accelerator_mac.cc
index 2b37130506e297534a4382db4e07a01eedb4ae7c..8a61575c382a0d4f8ce22523a49b314a11d90b62 100644
--- a/media/gpu/vt_video_decode_accelerator_mac.cc
+++ b/media/gpu/vt_video_decode_accelerator_mac.cc
@@ -866,13 +866,15 @@ void VTVideoDecodeAccelerator::AssignPictureBuffers(
 
 void VTVideoDecodeAccelerator::ReusePictureBuffer(int32_t picture_id) {
   DCHECK(gpu_thread_checker_.CalledOnValidThread());
-  DCHECK(picture_info_map_.count(picture_id));
-  PictureInfo* picture_info = picture_info_map_.find(picture_id)->second.get();
-  picture_info->cv_image.reset();
-  picture_info->gl_image->Destroy(false);

[sandersd (OOO until July 31), 2016/08/12 22:03:19]

ccameron@: Are we relying on this to always happen? My change may remove this
for already-discarded picture buffers. If it does need to run in that case, do
we also need a Destroy()-time loop to do this to the rest?

[sandersd (OOO until July 31), 2016/08/12 22:56:39]

I realized there was a better factoring without this difference, should be
behaviorally identical now.

-  picture_info->gl_image = nullptr;
 
   if (assigned_picture_ids_.count(picture_id) != 0) {
+    auto it = picture_info_map_.find(picture_id);
+    DCHECK_NE(it, picture_info_map_.end());
+    PictureInfo* picture_info = it->second.get();
+    picture_info->cv_image.reset();
+    picture_info->gl_image->Destroy(false);
+    picture_info->gl_image = nullptr;
+
     available_picture_ids_.push_back(picture_id);
     ProcessWorkQueues();
   } else {
@@ -1024,8 +1026,9 @@ bool VTVideoDecodeAccelerator::SendFrame(const Frame& frame) {
     return false;
 
   int32_t picture_id = available_picture_ids_.back();
-  DCHECK(picture_info_map_.count(picture_id));
-  PictureInfo* picture_info = picture_info_map_.find(picture_id)->second.get();
+  auto it = picture_info_map_.find(picture_id);
+  DCHECK_NE(it, picture_info_map_.end());
+  PictureInfo* picture_info = it->second.get();
   DCHECK(!picture_info->cv_image);
   DCHECK(!picture_info->gl_image);