Set fixed size to true on NewTabPageRecyclerView.

Its size is not affected by the adapter contents so this can be true,
allowing for internal optimizations.

Review-Url: https://codereview.chromium.org/2399983004
Cr-Commit-Position: refs/heads/master@{#423854}

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageRecyclerView.java

@@ -80,6 +80,8 @@ public class NewTabPageRecyclerView extends RecyclerView {
         mToolbarHeight = res.getDimensionPixelSize(R.dimen.toolbar_height_no_shadow)
                 + res.getDimensionPixelSize(R.dimen.toolbar_progress_bar_height);
         mMaxHeaderHeight = res.getDimensionPixelSize(R.dimen.snippets_article_header_height);
+
+        setHasFixedSize(true);
     }
 
     public boolean isFirstItemVisible() {