Add support for logging additional metrics in UKM.

components/metrics/proto/ukm/source.proto

Index: components/metrics/proto/ukm/source.proto
diff --git a/components/metrics/proto/ukm/source.proto b/components/metrics/proto/ukm/source.proto
index e48f252cc9380fb6080affe4baa73ae9f9fc5470..ca1c24d3b2337c248e1a066ff72f0f1a5618d460 100644
--- a/components/metrics/proto/ukm/source.proto
+++ b/components/metrics/proto/ukm/source.proto
@@ -24,6 +24,28 @@ message Source {
   // events related to this Source will generally be relative to this timestamp.
   optional int64 navigation_time_msec = 3;
 
-  // Time between navigation and the first contentful paint, in milliseconds.
+  // Time between navigation and the first contentful paint, in
+  // milliseconds. Will be unset if the page load did not reach first contentful
+  // paint.
   optional int64 first_contentful_paint_msec = 4;
+
+  // Time between navigation and the first meaningful paint, in
+  // milliseconds. Will be unset if the page load did not reach first meaningful
+  // paint.
+  optional int64 experimental_first_meaningful_paint_msec = 5;
+
+  // Time between navigation and the start of parsing, in milliseconds. Will be
+  // unset if the page load did not reach parse start.
+  optional int64 parse_start_msec = 6;
+
+  // Total time spent on the page, from navigation start to the end of the
+  // page's lifetime.  The page lifetime ends when the first of the following
+  // events happens:
+  // * the load of the main resource fails
+  // * the page load is stopped
+  // * the tab hosting the page is closed
+  // * the render process hosting the page goes away
+  // * a new navigation which later commits is initiated in the same tab
+  // * the page is backgrounded
+  optional int64 total_time_msec = 7;
 }