[object-stats] Allow zooming in histograms

No-try: true
Tbr: cbruni@chromium.org
Bug: v8:7266
Change-Id: I65ad82a8ae7b2b499ba3f2bf9fbec178edf7616a
Reviewed-on: https://chromium-review.googlesource.com/876202Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50724}

tools/heap-stats/histogram-viewer.js

@@ -114,6 +114,7 @@ class HistogramViewer extends HTMLElement {
       legend: {position: 'top', maxLines: '1'},
       chartArea: {width: '85%', height: '85%'},
       bar: {groupWidth: '80%'},
+      explorer: {},
     };
     const chart = new google.visualization.BarChart(this.$('#chart'));
     this.show();