Declare providing extension capabilities in the manifest.

chrome/common/BUILD.gn

Index: chrome/common/BUILD.gn
diff --git a/chrome/common/BUILD.gn b/chrome/common/BUILD.gn
index 7de5abb887cdd1d02e3fa027d666e2de9e998ebf..d7a04031d0e42b7fdd3f7a32b823935744adb8df 100644
--- a/chrome/common/BUILD.gn
+++ b/chrome/common/BUILD.gn
@@ -112,6 +112,12 @@ static_library("common") {
     if (enable_media_router) {
       defines += [ "ENABLE_MEDIA_ROUTER=1" ]
     }
+    if (is_chromeos) {
+      sources +=
+          rebase_path(gypi_values.chrome_common_extensions_chromeos_sources,
+                      ".",
+                      "//chrome")
+    }
   }
 
   if (is_win || is_mac) {