Refactor histogram-set-view to an MVC pattern.

tracing/tracing/ui/side_panel/metrics_side_panel_test.html

Index: tracing/tracing/ui/side_panel/metrics_side_panel_test.html
diff --git a/tracing/tracing/ui/side_panel/metrics_side_panel_test.html b/tracing/tracing/ui/side_panel/metrics_side_panel_test.html
index 0d6f88a467d6fb560ea38d57c3b76c0ffd9d9ac2..93f50ccd39f53f76b39aaa110076c7ab2006acbc 100644
--- a/tracing/tracing/ui/side_panel/metrics_side_panel_test.html
+++ b/tracing/tracing/ui/side_panel/metrics_side_panel_test.html
@@ -37,11 +37,11 @@ tr.b.unittest.testSuite(function() {
 
   tr.metrics.MetricRegistry.register(testMetric);
 
-  test('instantiateCollapsed', function() {
+  test('instantiateCollapsed', async function() {
     var metricsPanel = document.createElement('tr-ui-sp-metrics-side-panel');
-    metricsPanel.currentMetricName_ = 'testMetric';
-    metricsPanel.model = createModel();
     this.addHTMLOutput(metricsPanel);
+    metricsPanel.currentMetricName_ = 'testMetric';
+    await metricsPanel.build(createModel());
 
     assert.isDefined(tr.b.findDeepElementMatchingPredicate(
         metricsPanel, elem => elem.textContent === 'test histogram'));