cros: Add UMA metrics in encryption migration UI.

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 2aa3c49632f13f4bfb80bb1864afa9ddedbe5ca3..05e18e877d24c9b282aef1587de92f4c7862c060 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9545,6 +9545,35 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Cryptohome.MigrationUI.ConsumedBatteryPercent" units="%">
+  <owner>fukino@chromium.org</owner>
+  <summary>
+    The amount of consumed battery level during cryptohome encryption migration.
+    This is logged when the battery level decreases during migration, and the
+    data is used to check if the minimum battery level required to start
+    migration is appropriate.
+  </summary>
+</histogram>
+
+<histogram name="Cryptohome.MigrationUI.FirstScreen"
+    enum="MigrationUIFirstScreen">
+  <owner>fukino@chromium.org</owner>
+  <summary>
+    The first screen in the encryption migration UI, which is shown when a user
+    attempts to log in to the system and old encryption (eCryptfs) is detedted.

[Ilya Sherman, 2017/04/28 21:07:52]

nit: s/detedted/detected

[fukino, 2017/04/29 14:40:31]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Cryptohome.MigrationUI.UserChoice"
+    enum="MigrationUIUserChoice">
+  <owner>fukino@chromium.org</owner>
+  <summary>
+    User's choice when the system is ready to migrate encryption. The user can
+    start migration or skip it. It is used to know how many users have skipped
+    migration.
+  </summary>
+</histogram>
+
 <histogram name="Cryptohome.TimeToCompleteDircryptoMigration" units="ms">
   <owner>dspaid@chromium.org</owner>
   <summary>
@@ -105843,6 +105872,17 @@ from previous Chrome versions.
   <int value="2" label="IPsec"/>
 </enum>
 
+<enum name="MigrationUIFirstScreen" type="int">
+  <int value="0" label="Ready"/>
+  <int value="1" label="Resume"/>
+  <int value="2" label="LowStorage"/>
+</enum>
+
+<enum name="MigrationUIUserChoice" type="int">
+  <int value="0" label="Update"/>
+  <int value="1" label="Skip"/>
+</enum>
+
 <enum name="MissingStartType" type="int">
   <int value="0" label="Nothing missing"/>
   <int value="1" label="Start missing"/>