Add support for multiple simultaneous subresource_filter::Configurations.

chrome/browser/component_updater/subresource_filter_component_installer.cc

Index: chrome/browser/component_updater/subresource_filter_component_installer.cc
diff --git a/chrome/browser/component_updater/subresource_filter_component_installer.cc b/chrome/browser/component_updater/subresource_filter_component_installer.cc
index 5016878ec0a13b95fea2a6f541acf3b5f0df1804..1c20d3324cad5a09df31565af3fb1ef2fb814d2b 100644
--- a/chrome/browser/component_updater/subresource_filter_component_installer.cc
+++ b/chrome/browser/component_updater/subresource_filter_component_installer.cc
@@ -112,13 +112,13 @@ std::string SubresourceFilterComponentInstallerTraits::GetName() const {
 
 // static
 std::string SubresourceFilterComponentInstallerTraits::GetInstallerTag() {
-  const auto configurations = subresource_filter::GetActiveConfigurations();
-  const std::string& ruleset_flavor =
-      configurations->the_one_and_only().ruleset_flavor;
+  std::string ruleset_flavor = subresource_filter::GetActiveConfigurations()
+                                   ->GetMostSpecificRulesetFlavor();
+
   if (ruleset_flavor.empty())
     return ruleset_flavor;
 
-  // We allow 4 ruleset flavor identifiers: a, b, c, d
+  // In addition to "", we allow 4 ruleset flavor identifiers: a, b, c, d.
   if (ruleset_flavor.size() == 1 && ruleset_flavor.at(0) >= 'a' &&
       ruleset_flavor.at(0) <= 'd') {
     return ruleset_flavor;