Doc Update: JSON must be string data only.

Change-Id: I63c240dde0ce245d32612464d9ebeb790c9be6ca

Author: labtopia

docs/html/guide/google/gcm/adv.jd

@@ -203,7 +203,7 @@ registerReceiver(mRetryReceiver, filter);
 <p>GCM allows a maximum of 4 different collapse keys to be used by the GCM server at any given time. In other words, the GCM server can simultaneously store 4 different send-to-sync messages, each with a different collapse key. If you exceed this number GCM will only keep 4 collapse keys, with no guarantees about which ones they will be.</p>
 
 <h3 id="payload">Messages with payload</h3>
-<p>Unlike a send-to-sync message, every &quot;message with payload&quot; (non-collapsible message) is delivered. The payload the message contains can be up to 4K. For example, here is a JSON-formatted message in an IM application in which spectators are discussing a sporting event:</p>
+<p>Unlike a send-to-sync message, every &quot;message with payload&quot; (non-collapsible message) is delivered. The payload the message contains can be up to 4kb. For example, here is a JSON-formatted message in an IM application in which spectators are discussing a sporting event:</p>
 
 <pre class="prettyprint pretty-json">{
   "registration_id" : "APA91bHun4MxP5egoKMwt2KZFBaFUH-1RYqx...",

docs/html/guide/google/gcm/gcm.jd

@@ -651,8 +651,8 @@ message sent by the application server. See <a href="adv.html#collapsible">Advan
   <tr>
     <td><code>data</code></td>
     <td>A JSON object whose fields represents the key-value pairs of the message's payload data. If present, the payload data it will be
-included in the Intent as application data, with the key being the extra's name. For instance, <code>"data":{"score":"3x1"}</code> would result in an intent extra named <code>score</code> whose value is the string <code>3x1</code>
-There is no limit on the number of key/value pairs, though there is a limit on the total size of the message. Optional.</td>
+included in the Intent as application data, with the key being the extra's name. For instance, <code>"data":{"score":"3x1"}</code> would result in an intent extra named <code>score</code> whose value is the string <code>3x1</code>. 
+There is no limit on the number of key/value pairs, though there is a limit on the total size of the message (4kb). Note that the values <em>must be enclosed by strings</em>. If you want to include objects or other non-string data types (such as integers or booleans), you have to do the conversion to string yourself. Optional.</td>
   </tr>
   <tr>
     <td><code>delay_while_idle</code></td>