Always build ChromeVox as compressed js

ChromeVox can be run as both compressed (minified js) and uncompressed. The latter facilitates faster development.

It appears that in some instances, with the kevin board in particular, gn evaluates the ChromeVox build file incorrectly.

The end result is we end up with both uncompressed and compressed js files in ChromeVox leading to duplicate js objects.

Bug: 868579
Test: clean build for
1. prior to this patch
2. after this patch

Before each deployment, ensure we delete the chromevox folder on-device. This should be equilvanet to a new image.

Change-Id: I64cf826bda9239edc7764ba598bfed6dd0572d56
Reviewed-on: https://chromium-review.googlesource.com/1165787Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581325}

chrome/browser/resources/chromeos/chromevox/BUILD.gn

@@ -14,7 +14,7 @@ assert(is_chromeos)
 declare_args() {
   # Whether to compress the main Chromevox javascript files or load the
   # modules individually from source files.
-  chromevox_compress_js = !is_debug
+  chromevox_compress_js = true
 }
 
 closure_library_dir =