libsysprof: use a{sv} for future profiler specific options

We may need this in the future to send backend-specific options to the
profiler peer.

src/libsysprof/sysprof-proxy-source.c

@@ -229,7 +229,7 @@ sysprof_proxy_source_monitor (SysprofProxySource *self,
                                             self->object_path,
                                             "org.gnome.Sysprof3.Profiler",
                                             "Start",
-                                            g_variant_new ("(h)", handle),
+                                            g_variant_new ("(a{sv}h)", NULL, handle),
                                             G_VARIANT_TYPE ("()"),
                                             G_DBUS_CALL_FLAGS_NO_AUTO_START,
                                             -1,

src/org.gnome.Sysprof3.Profiler.xml

@@ -2,9 +2,28 @@
 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
 <node>
   <interface name="org.gnome.Sysprof3.Profiler">
+    <!--
+      Start:
+      @options: an a{sv} of implementation specific options
+      @fd: a file-descriptor for the profiler to write to
+
+      Start the profiler if it is not running.
+
+      If the profiler is already running, this method should return
+      an error so that the caller knows not to call Stop().
+
+      It is also suggested that implementations disable profiling if
+      they lose the peer connection.
+    -->
     <method name="Start">
+      <arg type="a{sv}" name="options" direction="in"/>
       <arg type="h" name="fd" direction="in"/>
     </method>
+    <!--
+      Stop:
+
+      Stop the profiler if it is running.
+    -->
     <method name="Stop"/>
   </interface>
 </node>