Create LoadingDataCollector class and have observers rely on it instead of ResourcePrefetchPredictor

chrome/browser/predictors/loading_predictor.h

Index: chrome/browser/predictors/loading_predictor.h
diff --git a/chrome/browser/predictors/loading_predictor.h b/chrome/browser/predictors/loading_predictor.h
index 9bcdd81fec861b45e1897c201c14f70d8aaced53..8e18c6006ad1e5d8570670663e095c3fc7fd3c8b 100644
--- a/chrome/browser/predictors/loading_predictor.h
+++ b/chrome/browser/predictors/loading_predictor.h
@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/memory/weak_ptr.h"
+#include "chrome/browser/predictors/glowplug_collector.h"
 #include "chrome/browser/predictors/resource_prefetch_common.h"
 #include "chrome/browser/predictors/resource_prefetch_predictor.h"
 #include "components/keyed_service/core/keyed_service.h"
@@ -44,12 +45,14 @@ class LoadingPredictor : public KeyedService,
 
   // Don't use, internal only.
   ResourcePrefetchPredictor* resource_prefetch_predictor() const;
+  GlowplugCollector* glowplug_collector() const;
 
   // KeyedService:
   void Shutdown() override;
 
  private:
   std::unique_ptr<ResourcePrefetchPredictor> resource_prefetch_predictor_;
+  std::unique_ptr<GlowplugCollector> glowplug_collector_;

[alexilin, 2017/05/22 13:20:36]

We need to decide whether GlowplugCollector should be independent KeyedService
or it's okay for LoadingPredictor to own it. I don't have a strong preference. 
lizeb@ WDYT?

[Benoit L, 2017/05/22 13:37:16]

As its lifetime is 100% tied to LoadingPredictor, I would tend to keep it owned
by LoadingPredictor, at least for now.
If at some point we have a reason to have the lifetimes diverge, we can still
make it a service then.

But I'm not 100% set on this either :-)

[alexilin, 2017/05/23 08:24:37]

SGTM
Just one point in favor of separate lifetimes is that in LEARNING mode we would
be able to use GlowplugCollector without constructing LoadingPredictor.

 
   DISALLOW_COPY_AND_ASSIGN(LoadingPredictor);
 };