Use a predicate that isn't so granular during continuous read.

Currently, continuous read uses the Node predicate. We want to use the DOM_NODE predicate because it doesn't chunk up nodes quite as much. This results in smoother reading (e.g. not breaking apart between lines).much.

Review URL: https://codereview.chromium.org/1592513002

Cr-Commit-Position: refs/heads/master@{#370784}

chrome/browser/resources/chromeos/chromevox/cvox2/background/background.js

@@ -418,7 +418,7 @@ Background.prototype = {
               .go();
           prevRange = this.currentRange_;
           this.setCurrentRange(
-              this.currentRange_.move(cursors.Unit.NODE, Dir.FORWARD));
+              this.currentRange_.move(cursors.Unit.DOM_NODE, Dir.FORWARD));
 
           if (!this.currentRange_ || this.currentRange_.equals(prevRange))
             global.isReadingContinuously = false;