cros: Add UMA metrics in migration UI to get more information from migration failures.

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 56a5e0f31264c79a0bd2467a8dde1e4bbd1da036..1b2cd5e171ed1957525c0f218e2a62ff2efb6c9a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9788,6 +9788,27 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Cryptohome.MigrationUI.MigrationResult"
+    enum="MigrationUIMigrationResult">
+  <owner>fukino@chromium.org</owner>
+  <summary>
+    The result of encryption migration from eCryptfs to Ext4 dircrypto. The
+    recorded result is what the migration UI in Chrome side is notified from
+    cryptohomed.
+  </summary>
+</histogram>
+
+<histogram name="Cryptohome.MigrationUI.RemoveCryptohomeResult"
+    enum="MigrationUIRemoveCryptohomeResult">
+  <owner>fukino@chromium.org</owner>
+  <summary>
+    The result of the removal of user's cryptohome. When the migration UI is
+    notified that the migration failed, the UI tries to remove the user's
+    cryptohome to make sure that the user can create clean crytohome directory
+    in the next sign-in.
+  </summary>
+</histogram>
+
 <histogram name="Cryptohome.MigrationUI.UserChoice"
     enum="MigrationUIUserChoice">
   <owner>fukino@chromium.org</owner>