Flatten mash overlay back into Chrome overlay

chrome/app/mash/chrome_mash_content_browser_manifest_overlay.json

-// NOTE: This overlay is applied to content_browser_manifest.json on top of
-// src/chrome/browser/chrome_content_browser_manifest_overlay.json.
-//
-// The resulting manifest is output to
-// ${out}/Packages/chrome_mash_content_browser/manifest.json and is used as the
-// manifest for "content_browser" (i.e. the browser process) when Chrome
-// is run in a Mash environment.
-{
-  "interface_provider_specs": {
-    "service_manager:connector": {
-      "provides": {
-        "ash": [
-          "app_list::mojom::AppListPresenter"
-        ],
-        "ime:ime_driver": []
-      },
-      "requires": {
-        "accessibility_autoclick": [ "ash:autoclick" ],
-        "task_viewer": [ "mash:launchable" ],
-        "ui": [ "ime_registrar" ]
-      }
-    }
-  }
-}