[CCA] Don't send broadcast when capturing on platform app version

Currently the path to send broadcast when capturing only works on SWA.
Since we are about to deprecate the platform app version of CCA, it is
okay to only support this function on SWA but not platform app.

Bug: b/173559007
Test: Manually
Change-Id: Id33b6a88c4adafaf5725c5bd874b3d80166b9012
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2592295
Auto-Submit: Wei Lee <wtlee@chromium.org>
Commit-Queue: Shik Chen <shik@chromium.org>
Reviewed-by: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837864}

chromeos/components/camera_app_ui/camera_app_helper_impl.cc

@@ -195,6 +195,10 @@ void CameraAppHelperImpl::GetWindowStateController(
 
 void CameraAppHelperImpl::SendNewCaptureBroadcast(bool is_video,
                                                   const std::string& name) {
+  // This function is only supported on SWA.
+  if (camera_app_ui_ == nullptr) {
+    return;
+  }
   auto file_path = camera_app_ui_->delegate()->GetFilePathInArcByName(name);
   if (file_path.empty()) {
     LOG(ERROR) << "Drop the broadcast request due to invalid file path in ARC "