chromeos-dbus-bindings: Generate only single proxy accessor for singletons

For D-Bus objects with single fixed object path assume that they are
singletons and remove the object path parameter from the proxy
accessor ObjectManagerProxy::GetNNNProxy() method.

BUG=brillo:348
TEST=`FEATURES=test emerge-link chromeos-dbus-bindings`
     `FEATURES=test emerge-link peerd privetd buffet apmanager lorgnette`

Change-Id: I29419e2db5bd0fc8a4f508804c1e322c1880a3dd
Reviewed-on: https://chromium-review.googlesource.com/252422
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/chromeos-dbus-bindings/proxy_generator_unittest.cc b/chromeos-dbus-bindings/proxy_generator_unittest.cc
index f0615a9..a157656 100644
--- a/chromeos-dbus-bindings/proxy_generator_unittest.cc
+++ b/chromeos-dbus-bindings/proxy_generator_unittest.cc
@@ -756,12 +756,10 @@
     return dbus_object_manager_;
   }
 
-  org::chromium::Itf1Proxy* GetItf1Proxy(
-      const dbus::ObjectPath& object_path) {
-    auto p = itf1_instances_.find(object_path);
-    if (p != itf1_instances_.end())
-      return p->second.get();
-    return nullptr;
+  org::chromium::Itf1Proxy* GetItf1Proxy() {
+    if (itf1_instances_.empty())
+      return nullptr;
+    return itf1_instances_.begin()->second.get();
   }
   std::vector<org::chromium::Itf1Proxy*> GetItf1Instances() const {
     std::vector<org::chromium::Itf1Proxy*> values;
@@ -1103,12 +1101,10 @@
     return dbus_object_manager_;
   }
 
-  org::chromium::Itf1Proxy* GetItf1Proxy(
-      const dbus::ObjectPath& object_path) {
-    auto p = itf1_instances_.find(object_path);
-    if (p != itf1_instances_.end())
-      return p->second.get();
-    return nullptr;
+  org::chromium::Itf1Proxy* GetItf1Proxy() {
+    if (itf1_instances_.empty())
+      return nullptr;
+    return itf1_instances_.begin()->second.get();
   }
   std::vector<org::chromium::Itf1Proxy*> GetItf1Instances() const {
     std::vector<org::chromium::Itf1Proxy*> values;