Fix ChromeVox presubmit

common/tts_background.js:740: ERROR - [JSC_POSSIBLE_INEXISTENT_PROPERTY] Property phoneticCharacters never defined on Object
    if (!properties.phoneticCharacters) {
                    ^^^^^^^^^^^^^^^^^^

R=akihiroota@chromium.org, josiahk@chromium.org

Test: browser_tests --gtest_filter=ChromeVox*.*Phonetic*
Change-Id: Id8935556fbfb130561596c6a334369d1c979b50f
AX-Relnotes: n/a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417089
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808054}

chrome/browser/resources/chromeos/accessibility/chromevox/common/abstract_tts.js

@@ -557,3 +557,6 @@ AbstractTts.substitutionDictionaryRegexp_;
  */
 AbstractTts.repetitionRegexp_ =
     /([-\/\\|!@#$%^&*\(\)=_+\[\]\{\}.?;'":<>\u2022])\1{2,}/g;
+
+/** TTS phonetic-characters property. @type {string} */
+AbstractTts.PHONETIC_CHARACTERS = 'phoneticCharacters';

chrome/browser/resources/chromeos/accessibility/chromevox/common/tts_background.js

@@ -737,7 +737,7 @@ TtsBackground = class extends ChromeTtsBase {
     }
 
     // Only pronounce phonetic hints when explicitly requested.
-    if (!properties['phoneticCharacters']) {
+    if (!properties[AbstractTts.PHONETIC_CHARACTERS]) {
       return;
     }