fix deps for target api_registration.lib

Building api_registration.lib clean directly fails.

Repro steps:
1. rmdir /s/q out\default
2. gn gen out\default
3. autoninja.bat -C out\default obj/chrome/browser/apps/platform_apps/api/api_registration.lib153933

Change-Id: Ia4b24b3c9822c0586e93ff4931b18bc2471f7f30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153933Reviewed-by: David Bertoni <dbertoni@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Brian Manthos <brianman@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#760301}

chrome/browser/extensions/BUILD.gn

@@ -803,6 +803,7 @@ jumbo_static_library("extensions") {
     "//chrome/browser/web_applications/extensions",
     "//chrome/common/extensions/api:extensions_features",
     "//chrome/common/safe_browsing:proto",
+    "//chrome/services/app_service/public/mojom",
     "//chrome/services/removable_storage_writer/public/mojom",
     "//components/autofill/content/browser",
     "//components/bookmarks/browser",