Log Autofill.Quality.*.ByFieldType by predicted type for unknown data.

components/autofill/core/browser/field_types.h

Index: components/autofill/core/browser/field_types.h
diff --git a/components/autofill/core/browser/field_types.h b/components/autofill/core/browser/field_types.h
index cee305fcda51c25dfe6c443692ebd96ecd1e20a3..1b1ab9941b9b24ccefec38b3d309ac69766915a4 100644
--- a/components/autofill/core/browser/field_types.h
+++ b/components/autofill/core/browser/field_types.h
@@ -163,9 +163,14 @@ enum ServerFieldType {
   // forms.
   CONFIRMATION_PASSWORD = 95,
 
+  // The data entered by the user matches multiple pieces of autofill data,
+  // none of which were predicted by autofill. This value is used for metrics
+  // only, it is not a predicted nor uploaded type.
+  AMBIGUOUS_TYPE = 96,
+
   // No new types can be added without a corresponding change to the Autofill
   // server.
-  MAX_VALID_FIELD_TYPE = 96,
+  MAX_VALID_FIELD_TYPE = 97,
 };
 
 // The list of all HTML autocomplete field type hints supported by Chrome.