Use the WebKit default fonts when specifying generic font families.

ppapi/proxy/host_dispatcher.h

Index: ppapi/proxy/host_dispatcher.h
===================================================================
--- ppapi/proxy/host_dispatcher.h	(revision 86427)
+++ ppapi/proxy/host_dispatcher.h	(working copy)
@@ -27,6 +27,10 @@
 class SyncChannel;
 }
 
+namespace ppapi {
+struct Preferences;
+}
+
 namespace pp {
 namespace proxy {
 
@@ -48,7 +52,8 @@
   // transferred.
   virtual bool InitHostWithChannel(Delegate* delegate,
                                    const IPC::ChannelHandle& channel_handle,
-                                   bool is_client);
+                                   bool is_client,
+                                   const ppapi::Preferences& preferences);
 
   // The host side maintains a mapping from PP_Instance to Dispatcher so
   // that we can send the messages to the right channel.