Add the Sync.PassphraseType histogram.

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 639fcfeec78f196096e33dc98fc1994970c5cf30..c87bc90cb8bbbc7e75a3e17c64ce38b5bca2821a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -36511,6 +36511,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Sync.PassphraseType" enum="SyncPassphraseType">
+  <owner>maxbogue@chromium.org</owner>
+  <summary>
+    The active sync passphrase type at sync startup, if encryption is active.

[Nicolas Zea, 2014/12/05 00:53:20]

nit: encryption is always active, I'd just remove that clause.

[maxbogue, 2014/12/05 18:58:59]

Done. I forgot that KEYSTORE was for when the user hasn't entered their own
passphrase.

+  </summary>
+</histogram>
+
 <histogram name="Sync.PasswordAssociationTime" units="milliseconds">
   <owner>zea@chromium.org</owner>
   <summary>
@@ -56203,6 +56210,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="3" label="Not migrated for an unknown reason"/>
 </enum>
 
+<enum name="SyncPassphraseType" type="int">
+  <int value="0" label="IMPLICIT_PASSPHRASE"/>
+  <int value="1" label="KEYSTORE_PASSPHRASE"/>
+  <int value="2" label="FROZEN_IMPLICIT_PASSPHRASE"/>
+  <int value="3" label="CUSTOM_PASSPHRASE"/>
+</enum>
+
 <enum name="SyncSimpleConflictResolutions" type="int">
   <summary>
     Sync simple conflict resolutions. The codes are listed in