Update ActivityLog detection to use previous values, hrefs.

chrome/browser/extensions/activity_log/activity_actions.cc

Index: chrome/browser/extensions/activity_log/activity_actions.cc
diff --git a/chrome/browser/extensions/activity_log/activity_actions.cc b/chrome/browser/extensions/activity_log/activity_actions.cc
index efc6ea8b66d06ee557bad382ff8071bbedfdf16e..d30e9d9e96856d9114bb5b373ea1083e0812a9da 100644
--- a/chrome/browser/extensions/activity_log/activity_actions.cc
+++ b/chrome/browser/extensions/activity_log/activity_actions.cc
@@ -161,7 +161,8 @@ Action::InjectionType Action::DidInjectAd(
     return NO_AD_INJECTION;
 
   if (api_name_ == ad_injection_constants::kHtmlIframeSrcApiName ||
-      api_name_ == ad_injection_constants::kHtmlEmbedSrcApiName) {
+      api_name_ == ad_injection_constants::kHtmlEmbedSrcApiName ||
+      api_name_ == ad_injection_constants::kHtmlAnchorHrefApiName) {
     return CheckSrcModification();
   } else if (EndsWith(api_name_,
                       ad_injection_constants::kAppendChildApiSuffix,
@@ -418,10 +419,35 @@ void Action::MaybeUploadUrl(rappor::RapporService* rappor_service) const {
 }
 
 Action::InjectionType Action::CheckSrcModification() const {
-  bool injected_ad = arg_url_.is_valid() &&
-                     !arg_url_.is_empty() &&
-                     AdNetworkDatabase::Get()->IsAdNetwork(arg_url_);
-  return injected_ad ? INJECTION_NEW_AD : NO_AD_INJECTION;
+  const AdNetworkDatabase* database = AdNetworkDatabase::Get();
+
+  bool arg_url_valid = arg_url_.is_valid() && !arg_url_.is_empty();
+
+  GURL prev_url;
+  std::string prev_url_string;
+  if (args_.get() && args_->GetString(1u, &prev_url_string))
+    prev_url = GURL(prev_url_string);
+
+  bool prev_url_valid = prev_url.is_valid() && !prev_url.is_empty();
+
+  bool injected_ad = arg_url_valid && database->IsAdNetwork(arg_url_);
+  bool replaced_ad = prev_url_valid && database->IsAdNetwork(prev_url);
+
+  if (injected_ad && replaced_ad)
+    return INJECTION_REPLACED_AD;
+  if (injected_ad)
+    return INJECTION_NEW_AD;
+  if (replaced_ad)
+    return INJECTION_REMOVED_AD;
+
+  // If the extension replaced a valid URL with another valid URL for an iframe,
+  // embed, href, etc, then chances are it's ad injection (as there are few
+  // legitimate use cases for this). Log it as a likely one, which also helps
+  // us determine the effectiveness of our IsAdNetwork() recognition.
+  if (arg_url_valid && prev_url_valid)
+    return INJECTION_LIKELY_REPLACED_AD;
+
+  return NO_AD_INJECTION;
 }
 
 Action::InjectionType Action::CheckAppendChild() const {