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diff --git a/dom/heapsnapshot/tests/unit/test_DominatorTree_06.js b/dom/heapsnapshot/tests/unit/test_DominatorTree_06.js
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+++ b/dom/heapsnapshot/tests/unit/test_DominatorTree_06.js
@@ -0,0 +1,56 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Test that the retained size of a node is the sum of its children retained
+// sizes plus its shallow size.
+
+// Note that we don't assert directly, only if we get an unexpected
+// value. There are just way too many nodes in the heap graph to assert for
+// every one. This test would constantly time out and assertion messages would
+// overflow the log size.
+function fastAssert(cond, msg) {
+  if (!cond) {
+    ok(false, msg);
+  }
+}
+
+var COUNT = { by: "count", count: false, bytes: true };
+
+function run_test() {
+  var path = saveNewHeapSnapshot();
+  var snapshot = ChromeUtils.readHeapSnapshot(path);
+  var dominatorTree = snapshot.computeDominatorTree();
+
+  // Do a traversal of the dominator tree and assert the relationship between
+  // retained size, shallow size, and children's retained sizes.
+
+  var root = dominatorTree.root;
+  var stack = [root];
+  while (stack.length > 0) {
+    var top = stack.pop();
+
+    var children = dominatorTree.getImmediatelyDominated(top);
+
+    var topRetainedSize = dominatorTree.getRetainedSize(top);
+    var topShallowSize = snapshot.describeNode(COUNT, top).bytes;
+    fastAssert(topShallowSize <= topRetainedSize,
+               "The shallow size should be less than or equal to the " +
+               "retained size");
+
+    var sumOfChildrensRetainedSizes = 0;
+    for (var i = 0; i < children.length; i++) {
+      sumOfChildrensRetainedSizes += dominatorTree.getRetainedSize(children[i]);
+      stack.push(children[i]);
+    }
+
+    fastAssert(sumOfChildrensRetainedSizes <= topRetainedSize,
+               "The sum of the children's retained sizes should be less than " +
+               "or equal to the retained size");
+    fastAssert(sumOfChildrensRetainedSizes + topShallowSize === topRetainedSize,
+               "The sum of the children's retained sizes plus the shallow " +
+               "size should be equal to the retained size");
+  }
+
+  ok(true, "Successfully walked the tree");
+  do_test_finished();
+}