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

chrome/browser/extensions/convert_user_script.cc

Index: chrome/browser/extensions/convert_user_script.cc
diff --git a/chrome/browser/extensions/convert_user_script.cc b/chrome/browser/extensions/convert_user_script.cc
index 0d79540bb249ba3bb5f21b1b4a844eb32cd721b9..f767a19553591f779e539174e45a5412ebdd5b6b 100644
--- a/chrome/browser/extensions/convert_user_script.cc
+++ b/chrome/browser/extensions/convert_user_script.cc
@@ -156,7 +156,8 @@ scoped_refptr<Extension> ConvertUserScriptToExtension(
 
   root->Set(keys::kContentScripts, content_scripts);
 
-  base::FilePath manifest_path = temp_dir.path().Append(kManifestFilename);
+  base::FilePath manifest_path = temp_dir.path().Append(
+      filenames::kManifestFilename);
   JSONFileValueSerializer serializer(manifest_path);
   if (!serializer.Serialize(*root)) {
     *error = ASCIIToUTF16("Could not write JSON.");