tools: Local tests for the speculative prefetch predictor.

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 1b131cc3d0ffb683842329d8d05e14d0d4b7d23b..dbf32c3ef2d769e641e873a5fc01ed39ec631e47 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.cc
+++ b/chrome/browser/predictors/resource_prefetch_predictor.cc
@@ -522,7 +522,8 @@ void ResourcePrefetchPredictor::OnMainFrameRequest(
   DCHECK_EQ(INITIALIZED, initialization_state_);
 
   const GURL& main_frame_url = request.navigation_id.main_frame_url;
-  StartPrefetching(main_frame_url);
+  if (!config_.ExternalPrefetchingOnly())

[pasko, 2016/11/17 15:59:04]

so 'external prefetch only' disables all prefetching or am I missing something?

[Benoit L, 2016/11/21 13:40:32]

It disables prefetches triggered by observing a navigation, but not ones from
directly calling ResourcePrefetchPredictor::StartPrefetching.

Added a comment in the place where this flag is defined.

+    StartPrefetching(main_frame_url);
 
   // Cleanup older navigations.
   CleanupAbandonedNavigations(request.navigation_id);