The root cause is that SpellCheckRequest::invoke performs an unnecessary and sometimes even incorrect check with |canCheckAsynchronously()|, which cancels the spell check request after step (4).

In |canCheckAsynchronously()|, the null pointer check on |range| or |range->firstNode()| is unnecessary, while checking |range->firstNode()->layoutObject()| is incorrect because that the range starts with an invisible node does not mean it's empty.

The check on |toElement(node)->isSpellCheckingEnabled()| should be done in |SpellChecker| instead, because |SpellChecker| typically passes a range that's not just a single node, and the check incorrectly cancels the request if the range passed is something like <div contenteditable spellcheck="false"><span spellcheck="true">foo</span></div>.

This function should be removed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7168dd4011adfe053b7a5c0f308fcf7b1495b31b

commit 7168dd4011adfe053b7a5c0f308fcf7b1495b31b
Author: xiaochengh <xiaochengh@chromium.org>
Date: Wed Aug 24 11:53:13 2016

Stop SpellCheckRequest from checking canCheckAsynchronously()

This patch removes static function canCheckAsynchronously() from
SpellCheckRequester.cpp and stops SpellCheckRequest from calling it.

The removed function is legacy code from the old age before the removal
of synchronous spell checking. In addition, the items checked by this
function do not make much sense now -- either incorrect or redundant.
Hence, the function is removed.

This patch is also a preparation for reducing the use of
TextCheckingParagraph: http://crrev.com/2273453003

BUG= 640456 
TEST=editing/spelling/paste_into_element_starting_with_invisible.html

Review-Url: https://codereview.chromium.org/2248413003
Cr-Commit-Position: refs/heads/master@{#414049}

[add] https://crrev.com/7168dd4011adfe053b7a5c0f308fcf7b1495b31b/third_party/WebKit/LayoutTests/editing/spelling/paste_into_element_starting_with_invisible.html
[modify] https://crrev.com/7168dd4011adfe053b7a5c0f308fcf7b1495b31b/third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp
[modify] https://crrev.com/7168dd4011adfe053b7a5c0f308fcf7b1495b31b/third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp
[modify] https://crrev.com/7168dd4011adfe053b7a5c0f308fcf7b1495b31b/third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.h