[Android O] Only delete legacy notification channels on upgrade

chrome/android/junit/src/org/chromium/chrome/browser/notifications/ChannelsInitializerTest.java

Index: chrome/android/junit/src/org/chromium/chrome/browser/notifications/ChannelsInitializerTest.java
diff --git a/chrome/android/junit/src/org/chromium/chrome/browser/notifications/ChannelsInitializerTest.java b/chrome/android/junit/src/org/chromium/chrome/browser/notifications/ChannelsInitializerTest.java
index 5e61cd61554dfdf3a9c2b113176cea57c9caf465..af096415a306d8af32856c5c2a4479055d6ec02c 100644
--- a/chrome/android/junit/src/org/chromium/chrome/browser/notifications/ChannelsInitializerTest.java
+++ b/chrome/android/junit/src/org/chromium/chrome/browser/notifications/ChannelsInitializerTest.java
@@ -5,7 +5,10 @@
 package org.chromium.chrome.browser.notifications;
 
 import static org.hamcrest.Matchers.containsInAnyOrder;
+import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.hasSize;
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.not;
 import static org.junit.Assert.assertThat;
 
 import android.app.NotificationManager;
@@ -33,6 +36,21 @@ public class ChannelsInitializerTest {
     }
 
     @Test
+    public void testDeleteLegacyChannels_noopOnCurrentDefinitions() throws Exception {
+        assertThat(mMockNotificationManager.getNotificationChannelIds(), is(empty()));
+
+        mChannelsInitializer.deleteLegacyChannels();
+        assertThat(mMockNotificationManager.getNotificationChannelIds(), is(empty()));
+
+        mChannelsInitializer.initializeStartupChannels();
+        assertThat(mMockNotificationManager.getNotificationChannelIds(), is(not(empty())));
+
+        int nChannels = mMockNotificationManager.getNotificationChannelIds().size();
+        mChannelsInitializer.deleteLegacyChannels();
+        assertThat(mMockNotificationManager.getNotificationChannelIds(), hasSize(nChannels));
+    }
+
+    @Test
     public void testInitializeStartupChannels() throws Exception {
         mChannelsInitializer.initializeStartupChannels();
         assertThat(mMockNotificationManager.getNotificationChannelIds(),