[Sessions] Add detailed logging of SessionRestore events.

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 8a25d233ba183c5e84cc217042f480bc794f41ad..6f72c78f8a954a27c977deb80f1f8e97d93a585b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -35531,6 +35531,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>How did the user interact with the SessionCrashed Bubble?</summary>
 </histogram>
 
+<histogram name="SessionRestore.Actions" enum="SessionRestoreActions">
+  <owner>chrisha@chromium.org</owner>
+  <summary>
+    The actions that have occurred in a session restore timeline. These are to
+    be interpreted as raw event counts.
+  </summary>
+</histogram>
+
 <histogram name="SessionRestore.AllTabsLoaded" units="milliseconds">
   <owner>jeremy@chromium.org</owner>
   <owner>sky@chromium.org</owner>
@@ -35661,6 +35669,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </details>
 </histogram>
 
+<histogram name="SessionRestore.TabActions" enum="SessionRestoreTabActions">
+  <owner>chrisha@chromium.org</owner>
+  <summary>
+    A breakdown of exactly how different tabs were treated during session
+    restore events.
+  </summary>
+</histogram>
+
 <histogram name="SessionRestore.TabClosedLongPeriod">
   <owner>jeremy@chromium.org</owner>
   <owner>sky@chromium.org</owner>
@@ -35678,6 +35694,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="SessionRestore.TabCount" units="tabs">
+  <owner>chrisha@chromium.org</owner>
+  <summary>
+    The number of tabs involved in a single session restore event.
+  </summary>
+</histogram>
+
 <histogram name="SessionStorageDatabase.Open" enum="SessionStorageDatabaseOpen">
   <owner>michaeln@chromium.org</owner>
   <summary>
@@ -61807,6 +61830,19 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="7" label="The bar with UMA opt-in option was shown."/>
 </enum>
 
+<enum name="SessionRestoreActions" type="int">
+  <int value="0" label="Session restore was started"/>
+  <int value="1" label="Session restore was interrupted by memory pressure"/>
+</enum>
+
+<enum name="SessionRestoreTabActions" type="int">
+  <int value="0" label="The tab created"/>
+  <int value="1" label="The foreground tabs loaded"/>
+  <int value="2" label="The background tabs loaded"/>
+  <int value="3" label="The loading of a tab was deferred"/>
+  <int value="4" label="A deferred tab was loaded due to user action"/>
+</enum>
+
 <enum name="SessionStartupPref" type="int">
   <int value="0" label="Open home page (unused)"/>
   <int value="1" label="Continue from last opened pages"/>