Add new pattern for creating downstream objects

chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java
index 17120e871caffbdcfa4cbda7b11184ede7e02aff..a93694822d631ff5aee07a77345b0f57019a0e4e 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeApplication.java
@@ -428,4 +428,44 @@ public class ChromeApplication extends ContentApplication {
     public AccountManagerDelegate createAccountManagerDelegate() {
         return new SystemAccountManagerDelegate(this);
     }
+
+    /**
+     * Selects an implementation of a class appropriate to this {@link ChromeApplication}.
+     * This should be overridden downstream.
+     * @param klass The class that the {@link ChromeApplication} may be asked to create an
+     *         implementaiton of.
+     */
+    protected <T> Class<? extends T> getImplementation(Class<T> klass) {
+        return klass;
+    }
+
+    /**
+     * Instantiates an object of a given type.
+     * This method exists as a utility to generate objects of types that have different
+     * implementations upstream and downstream.  To use this,
+     * - give the upstream class a public parameterless constructor,
+     * - give the downstream class a public parameterless constructor,
+     * - register the downstream implementation in the downstream getImplementation(), and
+     * - invoke this method on the appropriate class.
+     * @param klass The class for which the {@link ChromeApplication} should create an instance.
+     */
+    @SuppressWarnings("unchecked")
+    public static <T> T createObject(Class<T> klass) {
+        Class newKlass =
+                ((ChromeApplication) ContextUtils.getApplicationContext()).getImplementation(klass);
+
+        Object obj;
+        try {
+            obj = newKlass.newInstance();
+        } catch (InstantiationException e) {
+            throw new RuntimeException("Asked to create unexpected class: " + klass.getName(), e);
+        } catch (IllegalAccessException e) {
+            throw new RuntimeException("Asked to create unexpected class: " + klass.getName(), e);
+        }
+        if (!klass.isInstance(obj)) {
+            throw new RuntimeException("Created an instance of type " + obj.getClass().getName()
+                    + " when expected an instance of type " + klass.getName());
+        }
+        return (T) obj;
+    }
 }