Page Abort Events for relevant navigations

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index bf2dd23dba7c7ea3cddffb896bdcc83600b76347..7e646bf90c493f1e62b2e3ad4758a36bea4221ef 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -29939,6 +29939,26 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PageLoad.Timing2.NavigationToFirstBackground"
+    units="milliseconds">
+  <owner>bmcquade@chromium.org</owner>
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    Measures the time from navigation timing's navigation start to the time the
+    user first backgrounds the tab.

[Randy Smith (Not in Mondays), 2015/10/06 19:24:00]

I presume no entry is made in this histogram if the tab stays in the foreground?
 Also, what happens if we start in background, foreground, then background?

[Charlie Harrison, 2015/10/06 19:35:36]

No entry if tab stays in foreground. Start in background => foreground =>
background should not log anything either, I'll update these to say something
like "time to first background from initially foregrounded tab."

+  </summary>
+</histogram>
+
+<histogram name="PageLoad.Timing2.NavigationToFirstForeground"
+    units="milliseconds">
+  <owner>bmcquade@chromium.org</owner>
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    Measures the time from navigation timing's navigation start to the time the
+    user first foregrounds an initially backgrounded tab.

[Randy Smith (Not in Mondays), 2015/10/06 19:24:00]

Mirror set of questions (stays in background, start in foreground, background,
then foreground).

+  </summary>
+</histogram>
+
 <histogram name="PageLoad.Timing2.NavigationToFirstLayout" units="milliseconds">
   <owner>bmcquade@chromium.org</owner>
   <owner>csharrison@chromium.org</owner>
@@ -66843,6 +66863,10 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="3" label="Aborted load before first layout"/>
   <int value="4" label="Successful first layout (foreground)"/>
   <int value="5" label="Successful first layout (backgrounded)"/>
+  <int value="6" label="Aborted load before first layout (relevant page load)"/>
+  <int value="7" label="Relevant page load started in foreground"/>
+  <int value="8" label="Relevant page load started in backgound"/>
+  <int value="9" label="Received a bad timing IPC"/>
 </enum>
 
 <enum name="PageScaleFactorRange" type="int">