Add //examples and //services to root build target

This makes sure they are reachable in GN even if they aren't explicitly
depended on.

R=sky@chromium.org

Review URL: https://codereview.chromium.org/687823005
diff --git a/BUILD.gn b/BUILD.gn
index b85b88d..7cf6fcf 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -6,7 +6,9 @@
   testonly = true
 
   deps = [
+    "//examples",
     "//mojo",
+    "//services",
   ]
 
   if (!is_win) {