Revert of [NTP Snippets] Refresh the displayed snippets less frequently

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 44c6f0b27b66abb3bb2d6765aeb29dbd358d9446..bcf3b5ee27ba8f398e55ea6d01fc2e48026b875b 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
@@ -65,19 +65,18 @@
     }
 
     /**
-     * Sets the recipient for the fetched snippets.
+     * Sets the recipient for the fetched snippets. This method should be called only once.
      *
-     * An observer needs to be set before the native code attempts to transmit snippets them to
-     * java. Upon registration, the observer will be notified of already fetched snippets.
+     * 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, or {@code null} if we want to
-     *                 stop observing.
+     * @param observer object to notify when snippets are received.
      */
     public void setObserver(SnippetsObserver observer) {
-        assert mObserver == null || mObserver == observer;
+        assert mObserver == null;
 
         mObserver = observer;
-        nativeSetObserver(mNativeSnippetsBridge, observer == null ? null : this);
+        nativeSetObserver(mNativeSnippetsBridge, this);
     }
 
     @CalledByNative