Add entries for InputTo* page load metrics to histograms.xml.

This is a follow up to
https://chromium-review.googlesource.com/c/chromium/src/+/1155470
where the code to report the metrics was added.

Bug: 750639
Change-Id: Ib2ed87109d04837560bb6768020765e6d7183e8e
Reviewed-on: https://chromium-review.googlesource.com/1184969Reviewed-by: Gayane Petrosyan <gayane@chromium.org>
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585200}

tools/metrics/histograms/histograms.xml

@@ -68813,6 +68813,25 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Experimental.InputTiming.InputToNavigationStart"
+    units="ms" expires_after="2019-08-22">
+  <owner>sullivan@chromium.org</owner>
+  <summary>
+    The time between the OS-level input event that initiated a navigation, and
+    the navigation actually starting.
+  </summary>
+</histogram>
+
+<histogram
+    name="PageLoad.Experimental.InputTiming.InputToNavigationStart.Background"
+    units="ms" expires_after="2019-08-22">
+  <owner>sullivan@chromium.org</owner>
+  <summary>
+    The time between the OS-level input event that initiated a navigation, and
+    the navigation actually starting, for background loads.
+  </summary>
+</histogram>
+
 <histogram name="PageLoad.Experimental.NavigationToInteractive" units="ms">
   <owner>dproy@chromium.org</owner>
   <owner>tdresser@chromium.org</owner>
@@ -68940,6 +68959,46 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Experimental.PaintTiming.InputToFirstContentfulPaint"
+    units="ms" expires_after="2019-08-22">
+  <owner>sullivan@chromium.org</owner>
+  <summary>
+    The time between the OS-level input event that initiated a navigation, and
+    the first contentful paint of the page that was loaded in the navigation.
+  </summary>
+</histogram>
+
+<histogram
+    name="PageLoad.Experimental.PaintTiming.InputToFirstContentfulPaint.Background"
+    units="ms" expires_after="2019-08-22">
+  <owner>sullivan@chromium.org</owner>
+  <summary>
+    The time between the OS-level input event that initiated a navigation, and
+    the first contentful paint of the page that was loaded in the navigation,
+    for background loads.
+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Experimental.PaintTiming.InputToFirstPaint"
+    units="ms" expires_after="2019-08-22">
+  <owner>sullivan@chromium.org</owner>
+  <summary>
+    The time between the OS-level input event that initiated a navigation, and
+    the first paint of the page that was loaded in the navigation.
+  </summary>
+</histogram>
+
+<histogram
+    name="PageLoad.Experimental.PaintTiming.InputToFirstPaint.Background"
+    units="ms" expires_after="2019-08-22">
+  <owner>sullivan@chromium.org</owner>
+  <summary>
+    The time between the OS-level input event that initiated a navigation, and
+    the first paint of the page that was loaded in the navigation, for
+    background loads.
+  </summary>
+</histogram>
+
 <histogram
     name="PageLoad.Experimental.PaintTiming.NavigationToFirstMeaningfulPaint"
     units="ms">