Add shouldComponentUpdate() methods to RoomView and TimelinePanel

This will avoid re-rendering the whole RoomView every time we get a scroll
event, and might even help with https://github.com/vector-im/vector-web/issues/1056.

src/ObjectUtils.js

@@ -77,3 +77,34 @@ module.exports.getKeyValueArrayDiffs = function(before, after) {
 
     return results;
 };
+
+/**
+ * Shallow-compare two objects for equality: each key and value must be
+ * identical
+ */
+module.exports.shallowEqual = function(objA, objB) {
+    if (objA === objB) {
+        return true;
+    }
+
+    if (typeof objA !== 'object' || objA === null ||
+          typeof objB !== 'object' || objB === null) {
+        return false;
+    }
+
+    var keysA = Object.keys(objA);
+    var keysB = Object.keys(objB);
+
+    if (keysA.length !== keysB.length) {
+        return false;
+    }
+
+    for (var i = 0; i < keysA.length; i++) {
+        var key = keysA[i];
+        if (!objB.hasOwnProperty(key) || objA[key] !== objB[key]) {
+            return false;
+        }
+    }
+
+    return true;
+};