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..896f9495dd76d38c5cc73b80b6dee36e0acfea5e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -27677,6 +27677,32 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram
+    name="PasswordManager.KeychainMigration.NumChromeOwnedFailedPasswords">

[Ilya Sherman, 2015/06/29 23:10:52]

nit: Maybe "NumChromeOwnedInaccessiblePasswords" would be a clearer name, if
this isn't strictly a subset of "NumFailedPasswords"?  The current names make it
seem like this should be a strict subset.

[vasilii, 2015/06/30 08:45:49]

Done.

+  <owner>vasilii@chromium.org</owner>
+  <summary>
+    After migration from the Mac Keychain fails, records the number of passwords
+    in the Keychain 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
+    in the Chrome Password Manager database which values in the Keychain are not

[Ilya Sherman, 2015/06/29 23:10:52]

nit: "which values" -> "for which the corresponding values"

[vasilii, 2015/06/30 08:45:49]

Done.

+    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 database to be migrated.

[Ilya Sherman, 2015/06/29 23:10:52]

nit: Please clarify that there is no partial migration, so this is the total
number of passwords in the DB.

[vasilii, 2015/06/30 08:45:49]

Done.

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