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

shell/android/apk/src/org/chromium/mojo/shell/ShellService.java

Index: shell/android/apk/src/org/chromium/mojo/shell/ShellService.java
diff --git a/shell/android/apk/src/org/chromium/mojo/shell/ShellService.java b/shell/android/apk/src/org/chromium/mojo/shell/ShellService.java
index b2bfda62b7dd1f2b927fc1b371c9028399f5bf32..f996dd38b6508066e25c762f57e53e61d7827eed 100644
--- a/shell/android/apk/src/org/chromium/mojo/shell/ShellService.java
+++ b/shell/android/apk/src/org/chromium/mojo/shell/ShellService.java
@@ -263,6 +263,10 @@ public class ShellService extends Service {
         return ShellImpl.INSTANCE;
     }
 
+    void surfaceAvailable() {
+        nativeSurfaceAvailable();
+    }
+
     private static File getLocalAppsDir(Context context) {
         return context.getDir(LOCAL_APP_DIRECTORY, Context.MODE_PRIVATE);
     }
@@ -304,4 +308,6 @@ public class ShellService extends Service {
 
     private static native void nativeConnectToApplication(
             String applicationURL, int servicesHandle, int exposedServicesHandle);
+
+    private static native void nativeSurfaceAvailable();
 }