Fix a crash by AdvanceToNextMisspelling command (⌘-;) with empty INPUT

third_party/WebKit/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 512 matching lines @@
     cursor: auto;
     padding: 2px;
     white-space: pre-wrap;
     word-wrap: break-word;
 }
 
 ::-webkit-input-placeholder {
     -webkit-text-security: none;
     color: darkGray;
     pointer-events: none !important;
+    -webkit-user-select: none;

[yosin_UTC9, 2016/02/09 05:06:13]

It is strange that we attempt to spell check "read-only" text,
input::-webkit-input-placeholder selector sets so.
We should fix |advanceToNextMisspelling()| not to attempt checking spell for
"read-only" text rather than make placeholder unselectable to make user created
INPUT element not to crash.

[tkent, 2016/02/09 05:09:26]

I see. So, the following code in SpellChecker::advanceToNextMisspelling()
doesn't check editability.  I'll investigate it.

    // If spellingSearchRange starts in the middle of a word, advance to the
    // next word so we start checking at a word boundary. Going back by one char
    // and then forward by a word does the trick.
    if (startedWithSelection) {
    VisiblePosition oneBeforeStart =
previousPositionOf(createVisiblePosition(spellingSearchStart));
        if (oneBeforeStart.isNotNull())
            spellingSearchStart =
endOfWord(oneBeforeStart).toParentAnchoredPosition();
        // else we were already at the start of the editable node
    }

 }
 
 input::-webkit-input-placeholder {
     line-height: initial;
     white-space: pre;
     word-wrap: normal;
     overflow: hidden;
     -webkit-user-modify: read-only !important;
 }
 
@@ skipping 573 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. */