Add DCHECK ensuring textures are present after WrapNativeTextures().

BUG=864145
TEST=none

Change-Id: I6bb241e52a2a6e8ef7841d4a0b76cb3dfa88b2c5
Reviewed-on: https://chromium-review.googlesource.com/1153618Reviewed-by: Dan Sanders <sandersd@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578842}

media/base/video_frame.cc

@@ -232,6 +232,10 @@ scoped_refptr<VideoFrame> VideoFrame::WrapNativeTextures(
   memcpy(&frame->mailbox_holders_, mailbox_holders,
          sizeof(frame->mailbox_holders_));
   frame->mailbox_holders_release_cb_ = std::move(mailbox_holder_release_cb);
+
+  // Wrapping native textures should... have textures. https://crbug.com/864145.
+  DCHECK(frame->HasTextures());
+
   return frame;
 }