Resize video elements when step is displayed.

The videos have to be resized after each step is displayed,
because they are sized to fit into their container at load time,
but since the container isn't visible at load time, the videos
end up with wrong dimensions.

Trigger video resize after displaying each step.

problem_builder/public/js/mentoring_with_steps.js

@@ -270,8 +270,8 @@ function MentoringWithStepsBlock(runtime, element) {
 
     function showActiveStep() {
         var step = steps[activeStep];
-        step.updatePlots();
         $(step.element).show();
+        step.updateChildren();
     }
 
     function onChange() {

problem_builder/public/js/step.js

 function MentoringStepBlock(runtime, element) {
 
     var children = runtime.children(element);
-    var plots = [];
-    for (var i in children) {
-        var child = children[i];
-        var blockType = $(child.element).data('block-type');
-        if (blockType === 'sb-plot') {
-            plots.push(child);
-        }
-    }
 
     var submitXHR, resultsXHR,
         message = $(element).find('.sb-step-message');
@@ -21,6 +13,14 @@ function MentoringStepBlock(runtime, element) {
         }
     }
 
+    function updateVideo(video) {
+        video.resizer.align();
+    }
+
+    function updatePlot(plot) {
+        plot.update();
+    }
+
     return {
 
         initChildren: function(options) {
@@ -103,13 +103,18 @@ function MentoringStepBlock(runtime, element) {
             return $('.sb-step', element).data('has-question')
         },
 
-        updatePlots: function() {
-            if (plots) {
-                for (var i in plots) {
-                    var plot = plots[i];
-                    plot.update();
-                }
+        updateChildren: function() {
+            children.forEach(function(child) {
+                var type = $(child.element).data('block-type');
+                switch (type) {
+                case 'video':
+                    updateVideo(child);
+                    break;
+                case 'sb-plot':
+                    updatePlot(child);
+                    break;
                 }
+            });
         }
 
     };