Introduce a hash_of_hashes dictionary.

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 6b445183c65c64fe44cf659232b70a454ceae6c1..b0c23b64d25efd96047eab53ca14822d533d542a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -16846,6 +16846,10 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Settings.HashesDictionaryTrusted" enum="BooleanValid">
+  <summary>Whether the hashes dictionary for this profile is trusted.</summary>

[Alexei Svitkine (slow), 2014/01/08 21:19:36]

Mention when this is logged. (On profile prefs load?)

+</histogram>
+
 <histogram name="Settings.HomePageDomain" enum="OmniboxSearchEngine">
   <obsolete>
     Deprecated in Chrome 30.  Replaced by Settings.HomePageEngineType.
@@ -17018,6 +17022,15 @@ other types of suffix sets.
   <summary>The id of a tracked preference which was reset by Chrome.</summary>
 </histogram>
 
+<histogram name="Settings.TrackedPreferenceTrustedInitialized"
+    enum="TrackedPreference">
+  <summary>
+    The id of a tracked preference for which we do not have a MAC, but are
+    willing to seed blindly as either (1) the current MACs are trusted and this
+    is a newly tracked pref or (2) its value is NULL.
+  </summary>
+</histogram>
+
 <histogram name="Settings.TrackedPreferenceUnchanged" enum="TrackedPreference">
   <summary>
     The id of a tracked preference whose value has not changed since the last