Allow native_viewport to create new native windows on demand on Android.

shell/BUILD.gn

Index: shell/BUILD.gn
diff --git a/shell/BUILD.gn b/shell/BUILD.gn
index 1b071058240b96e336cb083a78018fdafb116d85..fc0e246148e511da767507bf649d49729ca61c88 100644
--- a/shell/BUILD.gn
+++ b/shell/BUILD.gn
@@ -289,6 +289,7 @@ if (is_android) {
       "android/apk/src/org/chromium/mojo/shell/SharingActivity.java",
       "android/apk/src/org/chromium/mojo/shell/SharingApplicationDelegate.java",
       "android/apk/src/org/chromium/mojo/shell/ShellService.java",
+      "android/apk/src/org/chromium/mojo/shell/ViewportActivity.java",
     ]
 
     deps = [
@@ -305,6 +306,7 @@ if (is_android) {
       "//services/sharing_sink:bindings_java",
       "//mojo/services/nfc/public/interfaces:interfaces_java",
       "//services/keyboard",
+      "//services/native_viewport:native_viewport_java",
     ]
   }
 
@@ -427,6 +429,7 @@ if (is_android) {
       ":resources",
       "//base:base_java",
       "//services/native_viewport:native_viewport_java",
+      "//shell/android/task_launcher",
       "//third_party/android_tools:google_play_services_default_resources",
     ]