Add instrumentation hooks to mesaure which subresource filter rules are used.

components/subresource_filter/core/common/document_subresource_filter.h

Index: components/subresource_filter/core/common/document_subresource_filter.h
diff --git a/components/subresource_filter/core/common/document_subresource_filter.h b/components/subresource_filter/core/common/document_subresource_filter.h
index 611707d9c3d3fb48b11d3f9691dfdecbe9ccf50d..4440973d3a65e5814e7607d1dc7b4d6a040977d0 100644
--- a/components/subresource_filter/core/common/document_subresource_filter.h
+++ b/components/subresource_filter/core/common/document_subresource_filter.h
@@ -57,6 +57,16 @@ class DocumentSubresourceFilter {
                             ActivationState activation_state,
                             scoped_refptr<const MemoryMappedRuleset> ruleset);
 
+  // Constructs a new filter that will:
+  //  -- Operate in a manner prescribed in |activation_state|.
+  //  -- Filter subresource loads in the scope of a document loaded from
+  //     |document_origin|.
+  //  -- Hold a reference to and use |ruleset| for its entire lifetime.
+  DocumentSubresourceFilter(url::Origin document_origin,
+                            ActivationState activation_state,
+                            scoped_refptr<const MemoryMappedRuleset> ruleset,
+                            std::unique_ptr<RuleRecorder> recorder);
+
   ~DocumentSubresourceFilter();
 
   ActivationState activation_state() const { return activation_state_; }