Show speech button for x-webkit-speech only if the field is editable and focused/hovered.

Source/core/css/html.css

 /*
  * The default style sheet used to render HTML.
  *
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 614 matching lines @@
 
 #if defined(ENABLE_INPUT_SPEECH) && ENABLE_INPUT_SPEECH
 input::-webkit-input-speech-button {
     -webkit-appearance: -webkit-input-speech-button;
     display: block;
     vertical-align: top;
     flex: none;
     -webkit-user-modify: read-only !important;
     -webkit-align-self: flex-start;
     margin: auto 0;
+    opacity: 0;
+    pointer-events: none;
+}
+
+input:enabled:read-write:-webkit-any(:focus,:hover)::-webkit-input-speech-button {
+    opacity: 1;
+    pointer-events: auto;
 }
 #endif
 
 keygen, select {
     border-radius: 5px;
 }
 
 keygen::-webkit-keygen-select {
     margin: 0px;
 }
@@ skipping 507 matching lines @@
 @page {
     /* FIXME: Define the right default values for page properties. */
     size: auto;
     margin: auto;
     padding: 0px;
     border-width: 0px;
 }
 
 /* noscript is handled internally, as it depends on settings. */