Implement Mac Keychain migration algorithm.

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 36452aa5c26c270e116b87468e7b6d6c86212d23..226890a35f00b5c8ecfab317adbf5795b6d15549 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -27677,6 +27677,31 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="PasswordManager.KeychainMigration.NumChromeOwnedFailedPasswords">
+  <owner>vasilii@chromium.org</owner>
+  <summary>
+    After migration from the Mac Keychain fails, records the number of passwords
+    owned by Chrome but not accessible by it.
+  </summary>
+</histogram>
+
+<histogram name="PasswordManager.KeychainMigration.NumFailedPasswords">
+  <owner>vasilii@chromium.org</owner>
+  <summary>
+    After migration from the Mac Keychain fails, records the number of passwords
+    not accessible by Chrome.
+  </summary>
+</histogram>
+
+<histogram name="PasswordManager.KeychainMigration.NumPasswordsOnFailure">
+  <owner>vasilii@chromium.org</owner>
+  <summary>
+    After migration from the Mac Keychain fails, records the number of passwords
+    in the Chrome Password Manager to be migrated.

[Ilya Sherman, 2015/06/27 05:45:34]

I'm not exactly sure how this number differs from the one above.  Could you
please clarify?

[vasilii, 2015/06/29 14:12:45]

Done. Note that there is no partial migration. NumPasswordsOnFailure shows the
total number of passwords with values hidden in the Keychain. NumFailedPasswords
are only those inaccessible by Chrome.

+  </summary>
+</histogram>
+
 <histogram name="PasswordManager.KWalletDeserializationStatus"
     enum="BooleanSuccess">
   <owner>gcasto@chromium.org</owner>