CrOS Media App: Tweak marker detection for splicing in Exif frames.

Rather than requiring input to start with the Jpeg DQT frames, detect
whether an APP1 frame is already present. This allows an in-between
layer to add an APP2 frame for the colorspace.

Bug: b/169717921
Change-Id: I326575b33df4d8e609c9ca4a6c810a55d8f093a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500390Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822120}

chromeos/components/media_app_ui/resources/js/piex_module.js

@@ -133,8 +133,8 @@ function makeOrientationIfdFrame(value) {
  * @return {!Promise<!File>}
  */
 async function extractFromRawImageBuffer(buffer) {
-  /** Quantization table. */
-  const DQT_MARKER = 0xffdb;
+  /** Application Segment Marker. */
+  const APP1_MARKER = 0xffe1;
 
   /** SOI. Page 64. */
   const START_OF_IMAGE = 0xffd8;
@@ -171,9 +171,11 @@ async function extractFromRawImageBuffer(buffer) {
     return original('No SOI');
   }
 
-  // Files returned by Piex should begin immediately with JPEG headers.
-  if (view.getUint16(2) !== DQT_MARKER) {
-    return original('Unexpected marker');
+  // Files returned by Piex should begin immediately with JPEG headers (and the
+  // Define Quantization Table marker). If a layer between here and Piex has
+  // added its own APP marker segment(s), don't add a duplicate.
+  if (view.getUint16(2) === APP1_MARKER) {
+    return original('APP1 marker already present');
   }
 
   // Ignore the Start-Of-Image already in `jpegData` (TIFF_HEADER has one).