Pepper: Allow plugins to call PPB_UDP_Socket::SendTo multiple times.

ppapi/proxy/udp_socket_resource_base.h

Index: ppapi/proxy/udp_socket_resource_base.h
diff --git a/ppapi/proxy/udp_socket_resource_base.h b/ppapi/proxy/udp_socket_resource_base.h
index 1ed9bbfef521a127f31aaab3b1871ab000718d8c..a18950bc446b35803a2de783dee44a7d94c837da 100644
--- a/ppapi/proxy/udp_socket_resource_base.h
+++ b/ppapi/proxy/udp_socket_resource_base.h
@@ -45,6 +45,9 @@ class PPAPI_PROXY_EXPORT UDPSocketResourceBase: public PluginResource {
   // The maximum number of received packets that we allow instances of this
   // class to buffer.
   static const size_t kPluginReceiveBufferSlots;
+  // The maximum number of buffers that we allow instances of this class to be
+  // sending before we block the plugin.
+  static const size_t kPluginSendBufferSlots;
 
  protected:
   UDPSocketResourceBase(Connection connection,
@@ -111,7 +114,6 @@ class PPAPI_PROXY_EXPORT UDPSocketResourceBase: public PluginResource {
 
   scoped_refptr<TrackedCallback> bind_callback_;
   scoped_refptr<TrackedCallback> recvfrom_callback_;
-  scoped_refptr<TrackedCallback> sendto_callback_;
 
   char* read_buffer_;
   int32_t bytes_to_read_;
@@ -122,6 +124,8 @@ class PPAPI_PROXY_EXPORT UDPSocketResourceBase: public PluginResource {
 
   std::queue<RecvBuffer> recv_buffers_;
 
+  std::queue<scoped_refptr<TrackedCallback>> sendto_callbacks_;
+
   DISALLOW_COPY_AND_ASSIGN(UDPSocketResourceBase);
 };