Add FMP to DataReductionProxy UMA and to Pingback Metrics

components/data_reduction_proxy/proto/pageload_metrics.proto

Index: components/data_reduction_proxy/proto/pageload_metrics.proto
diff --git a/components/data_reduction_proxy/proto/pageload_metrics.proto b/components/data_reduction_proxy/proto/pageload_metrics.proto
index 641789f01dcbbc346421833fba6384268d09e8c8..7a09418786e875f2cd5749e5b72023a97c9522a8 100644
--- a/components/data_reduction_proxy/proto/pageload_metrics.proto
+++ b/components/data_reduction_proxy/proto/pageload_metrics.proto
@@ -61,11 +61,14 @@ message PageloadMetrics {
   optional int32 compressed_page_size_bytes = 11;
 
   // The effective connection type at the start of the navigation.
   optional EffectiveConnectionType effective_connection_type = 12;
 
   // The amount of time the parser was blocked by loading script.
   optional Duration parse_blocked_on_script_load_duration = 13;
 
   // Time until parsing finished.
   optional Duration parse_stop = 14;
+
+  // Time to first meaningful paint.
+  optional Duration time_to_first_meaningful_paint = 15;

[Bryan McQuade, 2016/09/25 23:39:18]

I'd name this experimental_time_to_first_meaningful_paint if you decide you want
to log this while it is still experimental and subject to being changed.

[RyanSturm, 2016/09/26 20:15:51]

Done.

 }