ime: Return 'success' argument for inputMethodPrivate.setCompositionRange.

The API is supposed to return a boolean 'success' value, but we forgot to.

Bug: 1141347
Change-Id: I9f06828e5219209972d478becab515c5b7240062
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505856
Auto-Submit: Darren Shen <shend@chromium.org>
Reviewed-by: Keith Lee <keithlee@chromium.org>
Commit-Queue: Keith Lee <keithlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823408}

chrome/browser/chromeos/extensions/input_method_api.cc

@@ -461,7 +461,7 @@ InputMethodPrivateSetCompositionRangeFunction::Run() {
                                    params.selection_after, segments, &error)) {
     return RespondNow(Error(InformativeError(error, static_function_name())));
   }
-  return RespondNow(NoArguments());
+  return RespondNow(OneArgument(base::Value(true)));
 }
 
 ExtensionFunction::ResponseAction