Add another set of UMA histograms for tab switching on Android.

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 b440c9c353a457e3abe1cf36d8d8bc8e20b7cc55..bd2746eb2184370bf8cbd6f185c7c0601530edde 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5899,6 +5899,25 @@ other types of suffix sets.
   <summary>Error codes returned by sqlite the web db.</summary>
 </histogram>
 
+<histogram name="Tab.RestoreResult" enum="BooleanSuccess">
+  <summary>
+    When the browser restores a tab, whether the load was successful. Loads can
+    fail for instance when there is no connectivity.
+  </summary>
+</histogram>
+
+<histogram name="Tab.RestoreTime" units="ms">
+  <summary>Load time for a successful tab restore.</summary>
+</histogram>
+
+<histogram name="Tab.RestoreUserPersistence" enum="TabRestoreUserAction">
+  <summary>
+    When the browser restores a tab, whether the user waits for completion of
+    the load or if the user gives up by switching to another tab or leaving
+    Chrome.
+  </summary>
+</histogram>
+
 <histogram name="Tab.SwitchedToForegroundAge" units="ms">
   <summary>Age (in ms) when the tab was switched to foreground.</summary>
 </histogram>
@@ -9454,6 +9473,13 @@ other types of suffix sets.
   </int>
 </enum>
 
+<enum name="TabRestoreUserAction" type="int">
+  <int value="0" label="Wait for completion"/>
+  <int value="1" label="Switch to another tab"/>
+  <int value="2" label="Close tab"/>

[ppi, 2013/05/06 13:34:55]

It seems that none of these covers the case of the user going to tab switcher
and staying there (nice catch!).

Maybe we should simplify this to:
- Wait for completion
- Leave tab (close tab / switch tabs / go to tab switcher)
- Leave Chrome

?

[Philippe, 2013/05/06 13:47:51]

Good idea. I will update the downstream CL accordingly.

+  <int value="3" label="Leave Chrome"/>
+</enum>
+
 <enum name="TabSwitchedToForegroundLaunchedWithURL" type="int">
   <int value="0" label="Launched without an URL"/>
   <int value="1" label="Launched with an URL"/>