servo · bors-servo · Nov 4, 2015 · Nov 3, 2015
diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
@@ -791,8 +791,20 @@ impl<Window: WindowMethods> IOCompositor<Window> {
         self.pipeline_details.remove(&pipeline_id);
     }
 
-    fn update_layer_if_exists(&mut self, pipeline_id: PipelineId, properties: LayerProperties)
+    fn update_layer_if_exists(&mut self,
+                              pipeline_id: PipelineId,
+                              properties: LayerProperties)
                               -> bool {
+        if let Some(subpage_id) = properties.subpage_pipeline_id {
+            match self.find_layer_with_pipeline_and_layer_id(subpage_id, LayerId::null()) {
+                Some(layer) => {
+                    *layer.bounds.borrow_mut() = Rect::from_untyped(
+                        &Rect::new(Point2D::zero(), properties.rect.size));
+                }
+                None => warn!("Tried to update non-existent subpage root layer: {:?}", subpage_id),
+            }
+        }
+
         match self.find_layer_with_pipeline_and_layer_id(pipeline_id, properties.id) {
             Some(existing_layer) => {
                 existing_layer.update_layer(properties);

diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -4139,6 +4139,18 @@
             "url": "/_mozilla/mozilla/canvas/drawimage_html_image_9.html"
           }
         ],
+        "mozilla/iframe/resize_after_load.html": [
+          {
+            "path": "mozilla/iframe/resize_after_load.html",
+            "references": [
+              [
+                "/_mozilla/mozilla/iframe/resize_after_load_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/mozilla/iframe/resize_after_load.html"
+          }
+        ],
         "mozilla/webgl/clearcolor.html": [
           {
             "path": "mozilla/webgl/clearcolor.html",
@@ -8928,6 +8940,18 @@
           "url": "/_mozilla/mozilla/canvas/drawimage_html_image_9.html"
         }
       ],
+      "mozilla/iframe/resize_after_load.html": [
+        {
+          "path": "mozilla/iframe/resize_after_load.html",
+          "references": [
+            [
+              "/_mozilla/mozilla/iframe/resize_after_load_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/mozilla/iframe/resize_after_load.html"
+        }
+      ],
       "mozilla/webgl/clearcolor.html": [
         {
           "path": "mozilla/webgl/clearcolor.html",

diff --git a/tests/wpt/mozilla/tests/mozilla/iframe/resize_after_load.html b/tests/wpt/mozilla/tests/mozilla/iframe/resize_after_load.html
@@ -0,0 +1,24 @@
+<!doctype html>
+<html class="reftest-wait">
+    <head>
+        <meta charset=utf-8>
+        <title>Dynamically growing an iframe element</title>
+        <link rel=match href=/_mozilla/mozilla/iframe/resize_after_load_ref.html>
+    </head>
+
+    <body>
+        <iframe style="border: 0px; display: block; height: 100px; width: 50px" src="resources/green_inner_frame.html"></iframe>
+        <script>
+            var iframe = document.getElementsByTagName('iframe')[0];
+            iframe.onload = function() {
+                document.querySelector('iframe').style.width = "100px";
+
+                // We do this in a timeout, so that the compositor has a chance
+                // to update the layer tree.
+                setTimeout(function() {
+                    document.documentElement.classList.remove("reftest-wait");
+                }, 0);
+            }
+        </script>
+    </body>
+</html>
diff --git a/tests/wpt/mozilla/tests/mozilla/iframe/resize_after_load_ref.html b/tests/wpt/mozilla/tests/mozilla/iframe/resize_after_load_ref.html
@@ -0,0 +1,6 @@
+<!doctype html>
+<html>
+    <body>
+        <div style="height: 100px; width: 100px; background: green;"></div>
+    </body>
+</html>
diff --git a/tests/wpt/mozilla/tests/mozilla/iframe/resources/green_inner_frame.html b/tests/wpt/mozilla/tests/mozilla/iframe/resources/green_inner_frame.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<html>
+    <body style="background: green;">
+    </body>
+</html>