Add fake for InstanceIDWithSubtype.java, in order to re-use unit test

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
index ca3cc8f90f062a870b54f97dc3b4720f12251794..a806317ea626c02c4f6ea94ecd7e731d924b5254 100644
--- 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
@@ -26,9 +26,10 @@ public class InstanceIDWithSubtype extends InstanceID {
     private long mNativeInstanceIDAndroid;
     private final String mSubtype;
 
+    private static boolean sUseFakeForTesting = false;
     private static Map<String, InstanceIDWithSubtype> sSubtypeInstances = new HashMap<>();
 
-    private InstanceIDWithSubtype(long nativeInstanceIDAndroid, Context context, String subtype) {
+    protected InstanceIDWithSubtype(long nativeInstanceIDAndroid, Context context, String subtype) {
         super(context, subtype, null /* options */);
         mNativeInstanceIDAndroid = nativeInstanceIDAndroid;
         mSubtype = subtype;
@@ -43,7 +44,7 @@ public class InstanceIDWithSubtype extends InstanceID {
             }
             context = context.getApplicationContext();
 
-            if (sSubtypeInstances.isEmpty()) {
+            if (sSubtypeInstances.isEmpty() && !sUseFakeForTesting) {
                 // Warm up the InstanceID system, by getting then discarding the default InstanceID.
                 // This causes some important static fields to be initialized.
                 InstanceID.getInstance(context);
@@ -51,13 +52,28 @@ public class InstanceIDWithSubtype extends InstanceID {
 
             InstanceIDWithSubtype existing = sSubtypeInstances.get(subtype);
             if (existing == null) {
-                existing = new InstanceIDWithSubtype(nativeInstanceIDAndroid, context, subtype);
+                if (sUseFakeForTesting) {
+                    existing = new FakeInstanceIDWithSubtype(
+                            nativeInstanceIDAndroid, context, subtype);
+                } else {
+                    existing = new InstanceIDWithSubtype(nativeInstanceIDAndroid, context, subtype);
+                }
                 sSubtypeInstances.put(subtype, existing);
             }
             return existing;
         }
     }
 
+    @CalledByNative
+    public static void clearDataAndSetUseFakeForTesting(boolean useFake) {
+        sSubtypeInstances.clear();
+        sUseFakeForTesting = useFake;
+    }
+
+    public static Map<String, InstanceIDWithSubtype> getInstanceIDsForTesting() {
+        return sSubtypeInstances;
+    }
+
     @Override
     public void deleteInstanceID() throws IOException {
         synchronized (InstanceID.class) {