Don't forceUpdate the message panel on resize

We don't really need to forceUpdate() the entire timeline panel every time
something might resize it. It is sufficient to forceUpdate the ScrollPanel.

src/components/structures/MessagePanel.js

@@ -159,6 +159,18 @@ module.exports = React.createClass({
         }
     },
 
+    // makes the MessagePanel update itself after it is resized (due to other
+    // changes in the DOM)
+    onResize: function() {
+        if (!this.refs.scrollPanel) { return; }
+
+        // we don't need to forceUpdate ourselves here, but we do need to
+        // forceUpdate the scrollpanel, which will make the gemini panel update
+        // itself and trigger a scroll position check.
+        console.log("MessagePanel.onResize");
+        this.refs.scrollPanel.forceUpdate();
+    },
+
     _getEventTiles: function() {
         var EventTile = sdk.getComponent('rooms.EventTile');