Declare providing extension capabilities in the manifest.

extensions/common/manifest_constants.cc

Index: extensions/common/manifest_constants.cc
diff --git a/extensions/common/manifest_constants.cc b/extensions/common/manifest_constants.cc
index cb580dda4164c6f859cac4906fc3e09ef2b22df1..a9bab414cc0c60bc25ae273fd9c150f8f553d791 100644
--- a/extensions/common/manifest_constants.cc
+++ b/extensions/common/manifest_constants.cc
@@ -180,6 +180,9 @@ const char kWebviewAccessibleResources[] = "accessible_resources";
 const char kWebviewName[] = "name";
 const char kWebviewPartitions[] = "partitions";
 const char kWhitelist[] = "whitelist";
+#if defined(OS_CHROMEOS)
+const char kFileSystemProvider[] = "file_system_provider";
+#endif
 
 }  // namespace manifest_keys
 
@@ -698,6 +701,8 @@ const char kWebRequestConflictsWithLazyBackground[] =
 #if defined(OS_CHROMEOS)
 const char kIllegalPlugins[] =
     "Extensions cannot install plugins on Chrome OS";
+const char kInvalidFileSystemProvider[] =
+    "Invalid value for 'file_system_provider'.";
 #endif
 
 }  // namespace manifest_errors