Update ActivityLog detection to use previous values, hrefs.

chrome/browser/extensions/activity_log/activity_actions.h

Index: chrome/browser/extensions/activity_log/activity_actions.h
diff --git a/chrome/browser/extensions/activity_log/activity_actions.h b/chrome/browser/extensions/activity_log/activity_actions.h
index 626d05091cd8715427574bc513050ac7e7c87d5e..a2e3ea1afb1554161d3a34d6a13a4938ffadb578 100644
--- a/chrome/browser/extensions/activity_log/activity_actions.h
+++ b/chrome/browser/extensions/activity_log/activity_actions.h
@@ -47,11 +47,22 @@ class Action : public base::RefCountedThreadSafe<Action> {
 
   // The type of ad injection an action performed.
   enum InjectionType {
-    NO_AD_INJECTION = 0,    // No ad injection occurred.
-    INJECTION_NEW_AD,       // A new ad was injected.
-    INJECTION_REMOVED_AD,   // An ad was removed.
-    INJECTION_REPLACED_AD,  // An ad was replaced.
-    NUM_INJECTION_TYPES     // Place any new injection types above this entry.
+    // No ad injection occurred.
+    NO_AD_INJECTION = 0,
+    // A new ad was injected.
+    INJECTION_NEW_AD,
+    // An ad was removed.
+    INJECTION_REMOVED_AD,
+    // An ad was replaced.
+    INJECTION_REPLACED_AD,
+    // Something occurred which heuristically looks like an ad injection, but we
+    // didn't categorize it as such (likely because we didn't recognize it as
+    // an ad network). If our list is effective, this should be significantly
+    // lower than REPLACED_AD.
+    INJECTION_LIKELY_REPLACED_AD,
+
+    // Place any new injection types above this entry.
+    NUM_INJECTION_TYPES
   };
 
   // A useful shorthand for methods that take or return collections of Action