media/base: Fix VideoFrame::WrapVideoFrame().

WrapVideoFrame() currenlty copy data() regardless if source frame is
mappable or not. This is incorrect, it should copy data() when source
frame is mappable.

BUG=None
TEST=None

Change-Id: I2f6005114bbaef78c6facc20d431940a77780e81
Reviewed-on: https://chromium-review.googlesource.com/c/1352126Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Shuo-Peng Liao <deanliao@google.com>
Cr-Commit-Position: refs/heads/master@{#612107}

media/base/video_frame.cc

@@ -599,8 +599,10 @@ scoped_refptr<VideoFrame> VideoFrame::WrapVideoFrame(
   // Copy all metadata to the wrapped frame.
   wrapping_frame->metadata()->MergeMetadataFrom(frame->metadata());
 
-  for (size_t i = 0; i < NumPlanes(format); ++i) {
-    wrapping_frame->data_[i] = frame->data(i);
+  if (frame->IsMappable()) {
+    for (size_t i = 0; i < NumPlanes(format); ++i) {
+      wrapping_frame->data_[i] = frame->data(i);
+    }
   }
 
 #if defined(OS_LINUX)