[on-hold][subresource_filter] Add ActivationTracker to track all activated contents

components/subresource_filter/content/browser/content_subresource_filter_throttle_manager.h

Index: components/subresource_filter/content/browser/content_subresource_filter_throttle_manager.h
diff --git a/components/subresource_filter/content/browser/content_subresource_filter_throttle_manager.h b/components/subresource_filter/content/browser/content_subresource_filter_throttle_manager.h
index 446296538270edd2d17cbcb930676fe1ef1962b3..c8fc92f7174414e08748d5634a45ba3ced327255 100644
--- a/components/subresource_filter/content/browser/content_subresource_filter_throttle_manager.h
+++ b/components/subresource_filter/content/browser/content_subresource_filter_throttle_manager.h
@@ -47,6 +47,7 @@ class ContentSubresourceFilterThrottleManager
  public:
   // It is expected that the Delegate outlives |this|, and manages the lifetime
   // of this class.
+  // TODO(csharrison): Remove this in favor of the SubresourceFilterClient.
   class Delegate {
    public:
     // The embedder may be interested in displaying UI to the user when the
@@ -61,6 +62,8 @@ class ContentSubresourceFilterThrottleManager
     // Temporary method to help the delegate compute the activation decision.
     virtual void WillProcessResponse(
         content::NavigationHandle* navigation_handle) {}
+
+    virtual void OnPageActivated(const ActivationState& activation_state) {}
   };
 
   ContentSubresourceFilterThrottleManager(