Run google docs content script on Select-to-Speak load.

This allows Google Docs opened before Select-to-Speak was
enabled to still be read.

Bug: 882968
Change-Id: I723fcab46766983a8fe26477d2e9611e5bde1e9f
Reviewed-on: https://chromium-review.googlesource.com/1250601
Commit-Queue: Katie Dektar <katie@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595553}

chrome/browser/resources/chromeos/select_to_speak/select_to_speak.js

@@ -101,6 +101,7 @@ let SelectToSpeak = function() {
   this.prefsManager_ = new PrefsManager();
   this.prefsManager_.initPreferences();
 
+  this.runContentScripts_();
   this.setUpEventListeners_();
 };
 
@@ -398,6 +399,31 @@ SelectToSpeak.prototype = {
         [], this.prefsManager_.highlightColor());
   },
 
+  /**
+   * Runs content scripts that allow Select-to-Speak access to
+   * Google Docs content without a11y mode enabled, in every open
+   * tab. Should be run when Select-to-Speak starts up so that any
+   * tabs already opened will be checked.
+   * This should be kept in sync with the "content_scripts" section in
+   * the Select-to-Speak manifest.
+   * @private
+   */
+  runContentScripts_: function() {
+    chrome.tabs.query(
+        {
+          url: [
+            'https://docs.google.com/document*',
+            'https://docs.sandbox.google.com/*'
+          ]
+        },
+        (tabs) => {
+          tabs.forEach((tab) => {
+            chrome.tabs.executeScript(
+                tab.id, {file: 'select_to_speak_gdocs_script.js'});
+          });
+        });
+  },
+
   /**
    * Set up event listeners user input.
    */