Fix camera app ui bundle paths

out_camera_app_dir is constructed by:
'out_camera_app_dir = "$root_out_dir/resources/chromeos/camera"', which
already has a toolchain name inside the path if compiled by non-default
toolchain.

'out_camera_app_dir' in the grit_flags is supposed to be relative to
the target_gen_dir according to grit_rules.gni, therefore, when
rebasing, it needs to be rebased against root_out_dir instead of
root_build_dir so that the toolchain name bits can be stripped off.

Bug: 1129223
Change-Id: Ib2a5bf62f2f5957613398e03e20402c95896801e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2419658Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808615}

chromeos/components/camera_app_ui/resources/src/strings/BUILD.gn

@@ -127,8 +127,8 @@ grit("strings") {
 
   grit_flags = [
     "-E",
-    "out_camera_app_dir=" + rebase_path(out_camera_app_dir, root_build_dir),
+    "out_camera_app_dir=" + rebase_path(out_camera_app_dir, root_out_dir),
     "-E",
-    "gen_camera_app_dir=" + rebase_path(gen_camera_app_dir, root_build_dir),
+    "gen_camera_app_dir=" + rebase_path(gen_camera_app_dir, root_out_dir),
   ]
 }