Move ".crx"/".pem" constants and extension_filenames constants into extensions/common/constants.cc.

chrome/browser/extensions/extension_protocols.cc

Index: chrome/browser/extensions/extension_protocols.cc
diff --git a/chrome/browser/extensions/extension_protocols.cc b/chrome/browser/extensions/extension_protocols.cc
index 5bb7a98b7ae407eb64ea7edf79824070531e5e93..b1313981c72c415bee8e04e0e67184bc3e0ea797 100644
--- a/chrome/browser/extensions/extension_protocols.cc
+++ b/chrome/browser/extensions/extension_protocols.cc
@@ -482,7 +482,8 @@ ExtensionProtocolHandler::MaybeCreateJob(
 
   std::string path = request->url().path();
   if (path.size() > 1 &&
-      path.substr(1) == extension_filenames::kGeneratedBackgroundPageFilename) {
+      (path.substr(1) ==
+       extensions::filenames::kGeneratedBackgroundPageFilename)) {
     return new GeneratedBackgroundPageJob(
         request, network_delegate, extension, content_security_policy);
   }