Adds "tts" permission for Input Tools & XKB extension.

BUG=422869

Review URL: https://codereview.chromium.org/898443004

Cr-Commit-Position: refs/heads/master@{#314286}

chrome/browser/resources/chromeos/input_method/google_input_tools_manifest.json

@@ -18,6 +18,7 @@
     "inputMethodPrivate",
     "metricsPrivate",
     "tabs",
+    "tts",
     "unlimitedStorage",
     "virtualKeyboardPrivate"
   ],

chrome/browser/resources/chromeos/input_method/google_xkb_manifest.json

@@ -18,6 +18,7 @@
     "inputMethodPrivate",
     "metricsPrivate",
     "tabs",
+    "tts",
     "unlimitedStorage",
     "virtualKeyboardPrivate"
   ],