Add InstanceIDWithSubtype.java to allow an Instance ID per website

components/gcm_driver/instance_id/android/java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java

Index: components/gcm_driver/instance_id/android/java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java
diff --git a/components/gcm_driver/instance_id/android/java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java b/components/gcm_driver/instance_id/android/java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java
new file mode 100644
index 0000000000000000000000000000000000000000..8af5f6e3a3ab82669d5b8bb60d3fb302b45da8d7
--- /dev/null
+++ b/components/gcm_driver/instance_id/android/java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java
@@ -0,0 +1,72 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.components.gcm_driver.instance_id;
+
+import android.content.Context;
+import android.text.TextUtils;
+
+import com.google.android.gms.iid.InstanceID;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * InstanceID wrapper that allows multiple InstanceIDs to be created, depending
+ * on the provided subtype. Only for platforms-within-platforms like browsers.
+ */
+public class InstanceIDWithSubtype extends InstanceID {
+    private final String mSubtype;
+
+    /** Cached instances. May be accessed from multiple threads; synchronize on InstanceID.class. */
+    private static Map<String, InstanceIDWithSubtype> sSubtypeInstances = new HashMap<>();
+
+    private InstanceIDWithSubtype(Context context, String subtype) {
+        super(context, subtype, null /* options */);
+        mSubtype = subtype;
+    }
+
+    /**
+     * Returns an instance of this class. Unlike {@link InstanceID#getInstance(Context)}, it is not
+     * a singleton, but instead a different instance will be returned for each {@code subtype}.
+     */
+    public static InstanceIDWithSubtype getInstance(Context context, String subtype) {
+        if (TextUtils.isEmpty(subtype)) {
+            throw new IllegalArgumentException("subtype must not be empty");
+        }
+        context = context.getApplicationContext();
+
+        // Synchronize on the base class, to match the synchronized statements in
+        // InstanceID.getInstance.
+        synchronized (InstanceID.class) {
+            if (sSubtypeInstances.isEmpty()) {
+                // The static InstanceID.getInstance method performs some one-time initialization
+                // logic that is also necessary for users of this sub-class. To work around this,
+                // first get (but don't use) the default InstanceID.
+                InstanceID.getInstance(context);
+            }
+
+            InstanceIDWithSubtype existing = sSubtypeInstances.get(subtype);
+            if (existing == null) {
+                existing = new InstanceIDWithSubtype(context, subtype);
+                sSubtypeInstances.put(subtype, existing);
+            }
+            return existing;
+        }
+    }
+
+    @Override
+    public void deleteInstanceID() throws IOException {
+        // Synchronize on the base class, to match getInstance.
+        synchronized (InstanceID.class) {
+            sSubtypeInstances.remove(mSubtype);
+            super.deleteInstanceID();
+        }
+    }
+
+    public String getSubtype() {
+        return mSubtype;
+    }
+}