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 528307bf11c7c80718115396797cbad6bb7201ff..4873388c48c8749ba3b74127059f5b1665f484be 100644
--- a/extensions/common/manifest_constants.cc
+++ b/extensions/common/manifest_constants.cc
@@ -183,6 +183,9 @@ 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
 
@@ -709,6 +712,8 @@ 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