Allow EXIF to be absent in JEA IPC

This CL allows EXIF buffer to be absent in a JEA request.

BUG=b:79251580
TEST=Still capture with JEA works with EXIF length equaling 0

Change-Id: I4e9ff0a162bb3ac3f227f44716575234350eb2e0
Reviewed-on: https://chromium-review.googlesource.com/1061774Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Sheng-hao Tsao <shenghao@google.com>
Cr-Commit-Position: refs/heads/master@{#559416}

media/mojo/services/mojo_jpeg_encode_accelerator_service.cc

@@ -145,8 +145,11 @@ void MojoJpegEncodeAcceleratorService::EncodeWithFD(
 
   media::BitstreamBuffer output_buffer(buffer_id, output_shm_handle,
                                        output_buffer_size);
-  media::BitstreamBuffer exif_buffer(buffer_id, exif_shm_handle,
-                                     exif_buffer_size);
+  std::unique_ptr<media::BitstreamBuffer> exif_buffer;
+  if (exif_buffer_size > 0) {
+    exif_buffer = std::make_unique<media::BitstreamBuffer>(
+        buffer_id, exif_shm_handle, exif_buffer_size);
+  }
   gfx::Size coded_size(coded_size_width, coded_size_height);
 
   if (encode_cb_map_.find(buffer_id) != encode_cb_map_.end()) {
@@ -187,7 +190,7 @@ void MojoJpegEncodeAcceleratorService::EncodeWithFD(
       base::Passed(&input_shm)));
 
   DCHECK(accelerator_);
-  accelerator_->Encode(frame, kJpegQuality, &exif_buffer, output_buffer);
+  accelerator_->Encode(frame, kJpegQuality, exif_buffer.get(), output_buffer);
 #else
   NOTREACHED();
 #endif