Introduce IsMemberOfExtension function into ExtensionIMEUtil.

chromeos/ime/extension_ime_util.cc

Index: chromeos/ime/extension_ime_util.cc
diff --git a/chromeos/ime/extension_ime_util.cc b/chromeos/ime/extension_ime_util.cc
index 7e6d3ac267276eae811ff8575fdfb99ed12789a4..3c95751edd11022c9daa726fd8143994463e84da 100644
--- a/chromeos/ime/extension_ime_util.cc
+++ b/chromeos/ime/extension_ime_util.cc
@@ -25,5 +25,12 @@ bool IsExtensionIME(const std::string& input_method_id) {
                          true);  // Case sensitive.
 }
 
+bool IsMemberOfExtension(const std::string& input_method_id,
+                         const std::string& extension_id) {
+  return StartsWithASCII(input_method_id,
+                         kExtensionIMEPrefix + extension_id,
+                         true);  // Case sensitive.
+}
+
 }  // namespace extension_ime_util
 }  // namespace chromeos