feat: preliminary support for //extensions (#17440)

shell/common/extensions/api/BUILD.gn

@@ -0,0 +1,35 @@
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//extensions/buildflags/buildflags.gni")
+import("//tools/json_schema_compiler/json_features.gni")
+import("//tools/json_schema_compiler/json_schema_api.gni")
+
+assert(enable_extensions)
+
+################################################################################
+# Public Targets
+
+group("extensions_features") {
+  public_deps = [
+    ":manifest_features",
+
+    # TODO(devlin): It would be nicer to have this dependency hoisted up to
+    # //extensions/common (since that's where it's consumed), but there's some
+    # cycles to be resolved first.
+    "//extensions/common/api:extensions_features",
+  ]
+}
+
+################################################################################
+# Private Targets
+
+json_features("manifest_features") {
+  feature_type = "ManifestFeature"
+  method_name = "AddAtomManifestFeatures"
+  sources = [
+    "_manifest_features.json",
+  ]
+  visibility = [ ":extensions_features" ]
+}

shell/common/extensions/api/_manifest_features.json

@@ -0,0 +1,14 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This features file defines manifest keys implemented under src/chrome.
+// See chrome/common/extensions/api/_features.md to understand this file, as
+// well as feature.h, simple_feature.h, and feature_provider.h.
+
+{
+  "content_scripts": {
+    "channel": "stable",
+    "extension_types": ["extension", "legacy_packaged_app"]
+  }
+}