Reland of predictors: Basic browsertest checks predictor learning.

chrome/browser/predictors/resource_prefetch_predictor.h

Index: chrome/browser/predictors/resource_prefetch_predictor.h
diff --git a/chrome/browser/predictors/resource_prefetch_predictor.h b/chrome/browser/predictors/resource_prefetch_predictor.h
index 1de5b6bc52d231d732df53781ed306b621dfae00..b50a4f6b46164f99638883b3d8fd619dafb18847 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.h
+++ b/chrome/browser/predictors/resource_prefetch_predictor.h
@@ -163,6 +163,7 @@ class ResourcePrefetchPredictor
  private:
   friend class ::PredictorsHandler;
   friend class ResourcePrefetchPredictorTest;
+  friend class ResourcePrefetchPredictorBrowserTest;
 
   FRIEND_TEST_ALL_PREFIXES(ResourcePrefetchPredictorTest, DeleteUrls);
   FRIEND_TEST_ALL_PREFIXES(ResourcePrefetchPredictorTest,
@@ -365,6 +366,8 @@ class TestObserver {
       size_t url_visit_count,
       const ResourcePrefetchPredictor::PageRequestSummary& summary) {}
 
+  virtual void OnPredictorInitialized() {}
+
  protected:
   // |predictor| must be non-NULL and has to outlive the TestObserver.
   // Also the predictor must not have a TestObserver set.