[ios] Fix invocation of rebase_path() for some action

The parameters of a script invocation needs to be relative to the
directory where the script is invoked which is available as the
`root_build_dir` variable.

Using `root_out_dir` is incorrect as it has a different value for
secondary toolchains (i.e. current_toolchain != default_toolchain).

Bug: none
Change-Id: I573af8eb46c001fbedc641f5e47022f0424284c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489622
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819348}

build/config/ios/asset_catalog.gni

@@ -90,8 +90,8 @@ template("asset_catalog") {
       outputs = _outputs + [ _xcassets_dir ]
 
       args = [
-        rebase_path(get_path_info(_sources[0], "dir"), root_out_dir),
-        rebase_path(_output_dir, root_out_dir),
+        rebase_path(get_path_info(_sources[0], "dir"), root_build_dir),
+        rebase_path(_output_dir, root_build_dir),
       ]
     }
 

build/config/ios/rules.gni

@@ -927,8 +927,8 @@ template("ios_app_bundle") {
         sources = [ "${_default_variant.bundle_gen_dir}/$_bundle_short_name" ]
         outputs = [ "$root_out_dir/$_bundle_short_name" ]
 
-        args = rebase_path(sources, root_out_dir) +
-               rebase_path(outputs, root_out_dir)
+        args = rebase_path(sources, root_build_dir) +
+               rebase_path(outputs, root_build_dir)
       }
     }
   }