predictors: Disable URL-based learning by default.

chrome/browser/predictors/resource_prefetch_common.h

Index: chrome/browser/predictors/resource_prefetch_common.h
diff --git a/chrome/browser/predictors/resource_prefetch_common.h b/chrome/browser/predictors/resource_prefetch_common.h
index 3ec303d25d186fc7eced89b76116017943ed572b..6303eba4ac4849823f1040974cc690ee7f1eb569 100644
--- a/chrome/browser/predictors/resource_prefetch_common.h
+++ b/chrome/browser/predictors/resource_prefetch_common.h
@@ -7,7 +7,6 @@
 
 #include <stddef.h>
 
-#include "base/feature_list.h"
 #include "base/time/time.h"
 #include "components/sessions/core/session_id.h"
 #include "url/gurl.h"
@@ -25,6 +24,10 @@ extern const char kModeParamName[];
 extern const char kLearningMode[];
 extern const char kExternalPrefetchingMode[];
 extern const char kPrefetchingMode[];
+extern const char kKeyTypeParamName[];
+extern const char kUrlKeyType[];
+extern const char kHostKeyType[];
+extern const char kBothKeyType[];
 
 struct ResourcePrefetchPredictorConfig;
 
@@ -76,14 +79,17 @@ struct ResourcePrefetchPredictorConfig {
 
   // The mode the prefetcher is running in. Forms a bit map.
   enum Mode {
-    LEARNING = 1 << 0,
-    PREFETCHING_FOR_NAVIGATION = 1 << 2,  // Also enables LEARNING.
-    PREFETCHING_FOR_EXTERNAL = 1 << 3     // Also enables LEARNING.
+    URL_LEARNING = 1 << 0,
+    HOST_LEARNING = 1 << 1,
+    PREFETCHING_FOR_NAVIGATION = 1 << 2,
+    PREFETCHING_FOR_EXTERNAL = 1 << 3
   };
   int mode;
 
   // Helpers to deal with mode.
   bool IsLearningEnabled() const;
+  bool IsURLLearningEnabled() const;
+  bool IsHostLearningEnabled() const;
   bool IsPrefetchingEnabledForSomeOrigin(Profile* profile) const;
   bool IsPrefetchingEnabledForOrigin(Profile* profile,
                                      PrefetchOrigin origin) const;