Add ChromeVox panel and implement caption display functionality.

chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi

Index: chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi
diff --git a/chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi b/chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi
index 758a73e77efd9b6e0db8a86e145b72ac400cfe45..f7fd0bcabc62ce7653a9d18062095cab4c6c2358 100644
--- a/chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi
+++ b/chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi
@@ -22,6 +22,7 @@
     'generate_manifest_script_path': 'tools/generate_manifest.py',
     'is_guest_manifest%': 0,
     'is_chromevox_classic%': 0,
+    'is_chromeos%': 1,

[Peter Lundblad, 2015/11/06 15:00:58]

We already have a variable in gyp called 'chromeos', so it is a bit confusing to
add 'is_chromeos'. I think I understand why you do this, but it needs to be
clarified somehow. Perhaps a variable like chromevox_non_chromeos_build makes
more
sense.

[dmazzoni, 2015/11/06 21:01:01]

I ended up getting rid of the accessibilityFeatures permission because it turned
out to not reliably close ChromeVox. Apparently only one extension can have
"write" permission for a Chrome setting at a time.

Now clicking the 'close' button triggers the C++ code that hosts the panel to
close it, and that's reliable.

We'll have to figure out what to do for the webstore version. I could just hide
the close button.

   },
   'includes': [
     '../../../../../build/util/version.gypi',
@@ -42,6 +43,7 @@
         '<(generate_manifest_script_path)',
         '--is_guest_manifest=<(is_guest_manifest)',
         '--key=<(chromevox_extension_key)',
+        '--is_chromeos=<(is_chromeos)',
         '--is_chromevox_classic=<(is_chromevox_classic)',
         '--is_js_compressed=<(chromevox_compress_js)',
         '--set_version=<(version_full)',