Change the logic how Subesource Filter propagates activation.

components/subresource_filter/content/browser/content_subresource_filter_driver_factory.h

Index: components/subresource_filter/content/browser/content_subresource_filter_driver_factory.h
diff --git a/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.h b/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.h
index 2c9b4d43ff028fef7046d187a6785fe3786b0246..248d75bca76c03cad2925e0e743d197d503dc5e4 100644
--- a/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.h
+++ b/components/subresource_filter/content/browser/content_subresource_filter_driver_factory.h
@@ -68,6 +68,8 @@ class ContentSubresourceFilterDriverFactory
   // filtering for the lifetime of this WebContents.
   void AddHostOfURLToWhitelistSet(const GURL& url);
 
+  void AddToActivationHitsSet(const GURL& url);
+
   // Called when Safe Browsing detects that the |url| corresponding to the load
   // of the main frame belongs to the blacklist with |threat_type|. If the
   // blacklist is the Safe Browsing Social Engineering ads landing, then |url|
@@ -98,6 +100,7 @@ class ContentSubresourceFilterDriverFactory
 
   const HostSet& activation_set() const { return activate_on_hosts_; }
   const HostSet& whitelisted_set() const { return whitelisted_hosts_; }
+  const HostSet& hits_set() const { return hits_hosts_; }
   ActivationState activation_state() { return activation_state_; }
 
  private:
@@ -136,6 +139,8 @@ class ContentSubresourceFilterDriverFactory
 
   void set_activation_state(const ActivationState& new_activation_state);
 
+  bool IsHit(const GURL& url) const;
+
   static const char kWebContentsUserDataKey[];
 
   FrameHostToOwnedDriverMap frame_drivers_;
@@ -144,6 +149,10 @@ class ContentSubresourceFilterDriverFactory
   HostSet activate_on_hosts_;

[Jialiu Lin, 2016/10/07 21:54:27]

(Please correct me if I missed something) It seems this set never gets cleared
as long as the targeted WebContents is alive. I'm a little bit concerned that
this set might grow very big in some corner cases. 

[melandory, 2016/10/11 15:54:17]

Yes, it's true.
We had a discussion within the team and decided that we actually can get rid of
|activate_on_hosts_| and as result be more conservative with the activation.

   HostSet whitelisted_hosts_;
 
+  // List of hosts, where the Safe Browsing detected hit to the list of
+  // interest.
+  HostSet hits_hosts_;

[Jialiu Lin, 2016/10/07 21:54:27]

nit: maybe add more comments to explain the differences between hits_hosts_ and
activate_on_hosts_?  It takes me a while to figure out hits_hosts_ is a super
set of activate_on_hosts_. 

+
   ActivationState activation_state_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentSubresourceFilterDriverFactory);