Add @TargetApi to version dependent methods.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
index 19f5186b7c1738c7cfa31d78bdbed6b9c9e1a321..1a26272263bde66a1c71615c4594117bce4d7332 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser;
 
+import android.annotation.TargetApi;
 import android.app.Activity;
 import android.app.ActivityManager;
 import android.content.Context;
@@ -1509,6 +1510,7 @@ public class ChromeTabbedActivity extends ChromeActivity implements OverviewMode
      * Merges tabs from a second ChromeTabbedActivity instance if necesssary and calls
      * finishAndRemoveTask() on the other activity.
      */
+    @TargetApi(Build.VERSION_CODES.M)
     @VisibleForTesting
     public void maybeMergeTabs() {
         if (!FeatureUtilities.isTabModelMergingEnabled()) return;