[Autofill] Add metrics to determine whether the system AddressBook is accessible.

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 6d9ddf9ad688c7f68736b16b501c1c9331db05c7..0be4dbf159cae0f7ade8a3cf204f5304b9f24229 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1459,6 +1459,23 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Autofill.AddressBookAvailable" enum="BooleanAvailable">
+  <owner>isherman@chromium.org</owner>
+  <summary>
+    Whether the Mac AddressBook was available on an attempt to read data from
+    it.
+  </summary>
+</histogram>
+
+<histogram name="Autofill.AddressBookAvailableOnFirstAttempt"
+    enum="BooleanAvailable">
+  <owner>isherman@chromium.org</owner>
+  <summary>
+    Whether the Mac AddressBook was available on the *first* attempt to read

[Alexei Svitkine (slow), 2014/03/26 13:28:15]

Nit: Might be good to clarify what *first* means in this case. I originally read
this as *first* within a session, but it looks like you're saving a pref - so is
it "first attempt ever for a given profile"?

[Ilya Sherman, 2014/03/27 01:30:09]

Done.

+    data from it.
+  </summary>
+</histogram>
+
 <histogram name="Autofill.AddressSuggestionsCount">
   <owner>isherman@chromium.org</owner>
   <summary>