Fix wrong Nullable imported in StreamLifecycleManager.java

Guessing this was an IDE mistake :P. Came across this when doing
proguard testing.

Change-Id: Ib3ed490ff65635f6f6f8c725f522ed66ac0d5697
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752586Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686534}

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/NtpStreamLifecycleManager.java

@@ -5,9 +5,9 @@
 package org.chromium.chrome.browser.feed;
 
 import android.app.Activity;
+import android.support.annotation.Nullable;
 
 import com.google.android.libraries.feed.api.client.stream.Stream;
-import com.sun.istack.internal.Nullable;
 
 import org.chromium.base.VisibleForTesting;
 import org.chromium.chrome.browser.ntp.NewTabPage;

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/StreamLifecycleManager.java

@@ -6,9 +6,9 @@ package org.chromium.chrome.browser.feed;
 
 import android.app.Activity;
 import android.support.annotation.IntDef;
+import android.support.annotation.Nullable;
 
 import com.google.android.libraries.feed.api.client.stream.Stream;
-import com.sun.istack.internal.Nullable;
 
 import org.chromium.base.ActivityState;
 import org.chromium.base.ApplicationStatus;