Revert of [cast_channel] Move cast_channel related files from //extensions to //components

extensions/BUILD.gn

Index: extensions/BUILD.gn
diff --git a/extensions/BUILD.gn b/extensions/BUILD.gn
index f19ae04f3ac7800c0865d265b031563a4c90060d..2c71564389629e0c6b3b28e4f90a2ff8f39f61db 100644
--- a/extensions/BUILD.gn
+++ b/extensions/BUILD.gn
@@ -60,6 +60,8 @@
 static_library("test_support") {
   testonly = true
   sources = [
+    "browser/api/cast_channel/cast_test_util.cc",
+    "browser/api/cast_channel/cast_test_util.h",
     "browser/api/declarative/test_rules_registry.cc",
     "browser/api/declarative/test_rules_registry.h",
     "browser/api/dns/mock_host_resolver_creator.cc",
@@ -131,7 +133,6 @@
     ":extensions_resources",
     "//base",
     "//components/cast_certificate:test_support",
-    "//components/cast_channel:test_support",
     "//components/guest_view/browser:test_support",
     "//components/prefs:test_support",
     "//components/sync_preferences:test_support",
@@ -150,6 +151,7 @@
 
   public_deps = [
     "//content/public/browser",
+    "//extensions/common/api/cast_channel:cast_channel_proto",
   ]
 }