Use service process to collect printers.

chrome/common/service_messages.h

Index: chrome/common/service_messages.h
diff --git a/chrome/common/service_messages.h b/chrome/common/service_messages.h
index 1f05e6368bdb0666b8aef49c5ad3a85a0fa30580..c1b598b134b9c68295e8b681cf3aa6af69cc2592 100644
--- a/chrome/common/service_messages.h
+++ b/chrome/common/service_messages.h
@@ -37,6 +37,9 @@ IPC_MESSAGE_CONTROL0(ServiceMsg_GetCloudPrintProxyInfo)
 // Requests a message back with serialized UMA histograms.
 IPC_MESSAGE_CONTROL0(ServiceMsg_GetHistograms)
 
+// Requests a message back with all available printers.
+IPC_MESSAGE_CONTROL0(ServiceMsg_GetPrinters)
+
 // Tell the service process to shutdown.
 IPC_MESSAGE_CONTROL0(ServiceMsg_Shutdown)
 
@@ -53,3 +56,7 @@ IPC_MESSAGE_CONTROL1(ServiceHostMsg_CloudPrintProxy_Info,
 // Sent as a response to ServiceMsg_GetHistograms.
 IPC_MESSAGE_CONTROL1(ServiceHostMsg_Histograms,
                      std::vector<std::string> /* pickled_histograms */)
+
+// Sent as a response to ServiceMsg_GetPrinters.
+IPC_MESSAGE_CONTROL1(ServiceHostMsg_Printers,
+                     std::vector<std::string> /* printers */)