Add new NTP layout with snippet cards and hide it behind a flag

chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetsBridge.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetsBridge.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetsBridge.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetsBridge.java
index 64df7d0bf5ecc2e80aad60215441f03e8382f19b..cf110d09bf2d904611ad965ab7ebbd2f06fdf6c4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetsBridge.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetsBridge.java
@@ -4,9 +4,13 @@
 
 package org.chromium.chrome.browser.ntp.snippets;
 
+import org.chromium.base.Log;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.chrome.browser.profiles.Profile;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * Provides access to the snippets to display on the NTP using the C++ NTP Snippets Service
  */
@@ -14,14 +18,13 @@
     private static final String TAG = "SnippetsBridge";
 
     private long mNativeSnippetsBridge;
+    private SnippetsObserver mObserver;
 
     /**
      * An observer for notifying when new snippets are loaded
      */
     public interface SnippetsObserver {
-        @CalledByNative("SnippetsObserver")
-        public void onSnippetsAvailable(
-                String[] titles, String[] urls, String[] thumbnailUrls, String[] previewText);
+        public void onSnippetsReceived(List<SnippetArticle> snippets);
     }
 
     /**
@@ -29,28 +32,63 @@ public void onSnippetsAvailable(
      *
      * @param profile Profile of the user that we will retrieve snippets for.
      */
-    public SnippetsBridge(Profile profile, final SnippetsObserver observer) {
+    public SnippetsBridge(Profile profile) {
         mNativeSnippetsBridge = nativeInit(profile);
-        SnippetsObserver wrappedObserver = new SnippetsObserver() {
-            @Override
-            public void onSnippetsAvailable(
-                    String[] titles, String[] urls, String[] thumbnailUrls, String[] previewText) {
-                // Don't notify observer if we've already been destroyed.
-                if (mNativeSnippetsBridge != 0) {
-                    observer.onSnippetsAvailable(titles, urls, thumbnailUrls, previewText);
-                }
-            }
-        };
-        nativeSetObserver(mNativeSnippetsBridge, wrappedObserver);
     }
 
-    void destroy() {
+    /**
+     * Destroys the native service and unregisters observers. This object can't be reused to
+     * communicate with any native service and should be discarded.
+     */
+    public void destroy() {
         assert mNativeSnippetsBridge != 0;
         nativeDestroy(mNativeSnippetsBridge);
         mNativeSnippetsBridge = 0;
+        mObserver = null;
+    }
+
+    /**
+     * Sets the recipient for the fetched snippets. This method should be called only once.
+     *
+     * Before the observer is set, the native code will not attempt to transmit them to java. Upon
+     * registration, the observer will be notified of already fetched snippets.
+     *
+     * @param observer object to notify when snippets are received.
+     */
+    public void setObserver(SnippetsObserver observer) {
+        assert mObserver == null;
+
+        mObserver = observer;
+        nativeSetObserver(mNativeSnippetsBridge, this);
+    }
+
+    /**
+     * Unregisters the observer. Safe to call even if the bridge has been destroyed.
+     */
+    public void removeObserver() {
+        mObserver = null;
+    }
+
+    @CalledByNative
+    private void onSnippetsAvailable(String[] titles, String[] urls, String[] thumbnailUrls,
+            String[] previewText, long[] timestamps) {
+        // Don't notify observer if we've already been destroyed.
+        if (mNativeSnippetsBridge == 0) return;
+        if (mObserver == null) {
+            Log.w(TAG, "Snippets have been received while there is no observer to notify.");

[newt (away), 2016/03/31 04:16:22]

Keep comments as short as reasonable. The log buffer is limited in bytes, not
lines. E.g. "Snippets received before observer set"

[dgn, 2016/03/31 13:38:32]

Removed the comment and just used an assert. The observer's lifetime is longer
than the one of the bridge, and the observer is now removed on destroy, so it's
safe.

+            return;
+        }
+
+        List<SnippetArticle> newSnippets = new ArrayList<>(titles.length);
+        for (int i = 0; i < titles.length; i++) {
+            newSnippets.add(new SnippetArticle(
+                    titles[i], "", previewText[i], urls[i], thumbnailUrls[i], timestamps[i], i));
+        }
+
+        mObserver.onSnippetsReceived(newSnippets);
     }
 
     private native long nativeInit(Profile profile);
     private native void nativeDestroy(long nativeNTPSnippetsBridge);
-    private native void nativeSetObserver(long nativeNTPSnippetsBridge, SnippetsObserver observer);
+    private native void nativeSetObserver(long nativeNTPSnippetsBridge, SnippetsBridge bridge);
 }