predictors: Pass manifests from Bork to store in ResourcePrefetchPredictor.

components/precache/content/precache_manager.h

Index: components/precache/content/precache_manager.h
diff --git a/components/precache/content/precache_manager.h b/components/precache/content/precache_manager.h
index afd5e6c6e737de5006cfab24431c96ad684654da..3f678e9fcab99d7b4821fb42439692cc803dc2e9 100644
--- a/components/precache/content/precache_manager.h
+++ b/components/precache/content/precache_manager.h
@@ -55,6 +55,7 @@ namespace precache {
 
 class PrecacheDatabase;
 class PrecacheUnfinishedWork;
+class PrecacheManifest;
 
 extern const char kPrecacheFieldTrialName[];
 
@@ -73,6 +74,13 @@ class PrecacheManager : public KeyedService,
                         public PrecacheFetcher::PrecacheDelegate,
                         public base::SupportsWeakPtr<PrecacheManager> {
  public:
+  class Delegate {
+   public:
+    // Called when a precache manifest has been successfully fetched and parsed.
+    virtual void OnManifestFetched(const std::string& host,
+                                   const PrecacheManifest& manifest) = 0;
+  };
+
   typedef base::Callback<void(bool)> PrecacheCompletionCallback;
 
   PrecacheManager(content::BrowserContext* browser_context,
@@ -80,6 +88,7 @@ class PrecacheManager : public KeyedService,
                   const history::HistoryService* history_service,
                   const data_reduction_proxy::DataReductionProxySettings*
                       data_reduction_proxy_settings,
+                  Delegate* delegate,
                   const base::FilePath& db_path,
                   std::unique_ptr<PrecacheDatabase> precache_database);
   ~PrecacheManager() override;
@@ -153,6 +162,8 @@ class PrecacheManager : public KeyedService,
 
   // From PrecacheFetcher::PrecacheDelegate.
   void OnDone() override;
+  void OnManifestFetched(const std::string& host,
+                         const PrecacheManifest& manifest) override;
 
   // Registers the precache synthetic field trial for users whom the precache
   // task was run recently. |last_precache_time| is the last time precache task
@@ -219,6 +230,10 @@ class PrecacheManager : public KeyedService,
   const data_reduction_proxy::DataReductionProxySettings* const
       data_reduction_proxy_settings_;
 
+  // The Delegate corresponding to the browser context. Used to notify the
+  // browser about a new available manifest. May be null.
+  Delegate* delegate_;

[Benoit L, 2017/03/21 13:24:15]

I understand why this is fine here, as the service resolution mechanism enforces
a longer lifetime for the delegate than this service, but that's quite subtle.

Can you put a comment at the location where you provide the delegate, to make it
clear that's safe?

[alexilin, 2017/03/21 15:32:13]

Isn't it clear from DependsOn() list in factory class? 
There are other dependencies injected by a factory in the same way. And it seems
like it's a common practice in Chromium.
On the contrary, I'd suggest to add comment to PrecacheManger class that all
injected in constructor dependencies must outlive the class, WDYT?

[Benoit L, 2017/03/21 15:46:15]

Acknowledged.

+
   // The PrecacheFetcher used to precache resources. Should only be used on the
   // UI thread.
   std::unique_ptr<PrecacheFetcher> precache_fetcher_;