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

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 5881 matching lines @@
 </histogram>
 
 <histogram name="Sqlite.Thumbnail.Error" enum="SqliteErrorCode">
   <summary>Error codes returned by sqlite for the thumbnail db.</summary>
 </histogram>
 
 <histogram name="Sqlite.Web.Error" enum="SqliteErrorCode">
   <summary>Error codes returned by sqlite the web db.</summary>
 </histogram>
 
+<histogram name="Tab.RestoreResult" enum="TabRestoreResult">

[Ilya Sherman, 2013/05/01 01:16:05]

nit: Perhaps re-use the "BooleanSuccess" enum?

[Philippe, 2013/05/02 08:08:47]

Good point.

+  <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" unit="ms">

[Ilya Sherman, 2013/05/01 01:16:05]

This should be "units".  I'm surprised this wasn't caught by the presubmit
check... did you skip that check somehow?

[Philippe, 2013/05/02 08:08:47]

Good catch! The hook was run but the error wasn't propagated  correctly, see the
output:
INFO:root:Loading histograms.xml...
INFO:root:Pretty-printing...
ERROR:root:Unrecognized attribute unit in tag histogram
INFO:root:histograms.xml is correctly pretty-printed.

Presubmit checks took 2.2s to calculate.

Presubmit checks passed.

+  <summary>Load times for successful tab restores.</summary>

[Ilya Sherman, 2013/05/01 01:16:05]

Is this per-tab, or for a whole window, when restoring multiple tabs at once?

[Philippe, 2013/05/02 08:08:47]

I'm using singular now which should be less confusing.

+</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>
 
 <histogram name="Tab.SwitchedToForegroundLaunchedWithURL"
     enum="TabSwitchedToForegroundLaunchedWithURL">
   <summary>
     Each time a tab is brought to the foreground, this histogram indicates if
     chrome was launched without an URL (i.e., from the launcher), or with an URL
     (i.e., from another app).
@@ skipping 3535 matching lines @@
   </int>
   <int value="26" label="SQLITE_NOTADB">
     File opened that is not a database file
   </int>
   <int value="100" label="SQLITE_ROW">sqlite3_step() has another row ready</int>
   <int value="101" label="SQLITE_DONE">
     sqlite3_step() has finished executing
   </int>
 </enum>
 
+<enum name="TabRestoreResult" type="int">
+  <int value="0" label="Failed"/>
+  <int value="1" label="Succeeded"/>
+</enum>
+
+<enum name="TabRestoreUserAction" type="int">
+  <int value="0" label="WaitForCompletion"/>

[Ilya Sherman, 2013/05/01 01:16:05]

nit: "Wait for completion"

[Philippe, 2013/05/02 08:08:47]

Done.

+  <int value="1" label="SwitchToAnotherTab"/>

[Ilya Sherman, 2013/05/01 01:16:05]

nit: "Switch to another tab"

[Philippe, 2013/05/02 08:08:47]

Done.

+  <int value="2" label="LeaveChrome"/>

[Ilya Sherman, 2013/05/01 01:16:05]

nit: "Leave Chrome"

[Philippe, 2013/05/02 08:08:47]

Done.

+</enum>
+
 <enum name="TabSwitchedToForegroundLaunchedWithURL" type="int">
   <int value="0" label="Launched without an URL"/>
   <int value="1" label="Launched with an URL"/>
 </enum>
 
 <enum name="TabSwitchedToForegroundRevisit" type="int">
   <int value="0" label="First time"/>
   <int value="1" label="Revisit"/>
 </enum>
 
@@ skipping 1318 matching lines @@
 <fieldtrial name="SSLResumption">
   <group name="Resume_Handshake" label="Session Resumption"/>
   <group name="Full_Handshake" label="Full"/>
   <affected-histogram name="Net.SSL_Connection_Latency"/>
   <affected-histogram name="Net.SSL_Connection_Latency_Google"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>