Fix screenshots Data Table and Tile Map. Add comments.

test/functional/apps/visualize/_area_chart.js

@@ -115,6 +115,9 @@ define(function (require) {
           .then(function () {
             return visualizePage.waitForVisualization();
           })
+          // We have to sleep sometime between loading the saved visTitle
+          // and trying to access the chart below with getXAxisLabels
+          // otherwise it hangs.
           .then(function sleep() {
             return common.sleep(2000);
           })

test/functional/apps/visualize/_line_chart.js

@@ -119,6 +119,7 @@ define(function (require) {
           // it could also check the legend to verify the extensions
           var expectedChartData = ['jpg 9,109', 'css 2,159', 'png 1,373', 'gif 918', 'php 445'];
 
+          // sleep a bit before trying to get the chart data
           return common.sleep(3000)
           .then(function () {
             return visualizePage.getLineChartData()

test/functional/apps/visualize/_pie_chart.js

@@ -114,6 +114,7 @@ define(function (require) {
           .then(function waitForVisualization() {
             return visualizePage.waitForVisualization();
           })
+          // sleep a bit before trying to get the pie chart data below
           .then(function sleep() {
             return common.sleep(2000);
           })

test/functional/apps/visualize/_tile_map.js

@@ -107,6 +107,7 @@ define(function (require) {
           .then(function waitForVisualization() {
             return visualizePage.waitForVisualization();
           })
+          // sleep a bit before taking the screenshot or it won't show data
           .then(function sleep() {
             return common.sleep(4000);
           })