Reland of predictors: Basic browsertest checks predictor learning.

chrome/browser/predictors/resource_prefetch_predictor.cc

Index: chrome/browser/predictors/resource_prefetch_predictor.cc
diff --git a/chrome/browser/predictors/resource_prefetch_predictor.cc b/chrome/browser/predictors/resource_prefetch_predictor.cc
index 9c79a95f026f9cf1d65497884635281fa70811e3..c368a5256eee5bb2a1a10eac98afdebab8ba7d74 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.cc
+++ b/chrome/browser/predictors/resource_prefetch_predictor.cc
@@ -711,6 +711,9 @@ void ResourcePrefetchPredictor::OnHistoryAndCacheLoaded() {
         this, config_, profile_->GetRequestContext());
   }
   initialization_state_ = INITIALIZED;
+
+  if (observer_)
+    observer_->OnPredictorInitialized();
 }
 
 void ResourcePrefetchPredictor::CleanupAbandonedNavigations(