Decompose //extensions/browser/BUILD.gn

extensions/browser/api/system_storage/BUILD.gn

Index: extensions/browser/api/system_storage/BUILD.gn
diff --git a/components/leveldb/public/interfaces/BUILD.gn b/extensions/browser/api/system_storage/BUILD.gn
similarity index 52%
copy from components/leveldb/public/interfaces/BUILD.gn
copy to extensions/browser/api/system_storage/BUILD.gn
index 0b95cf4b365afc2bf68220e01f2eca7ac41d5b35..dbbef33c53e8c454df172ee5c48dc98779c1539c 100644
--- a/components/leveldb/public/interfaces/BUILD.gn
+++ b/extensions/browser/api/system_storage/BUILD.gn
@@ -2,14 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//mojo/public/tools/bindings/mojom.gni")
-
-mojom("interfaces") {
+source_set("system_storage") {
   sources = [
-    "leveldb.mojom",
+    "storage_info_provider.cc",
+    "storage_info_provider.h",
+    "system_storage_api.cc",
+    "system_storage_api.h",
   ]
 
   deps = [
-    "//components/filesystem/public/interfaces",
+    "//extensions/common/api",
   ]
 }