[WIP, not for review] Workaround for setComposition styling clobber

[WIP, not for review] Workaround for setComposition styling clobber

BUG=620549

[Changwan Ryu, 2016-09-07 04:14:39]

changwan@chromium.org changed reviewers:
+ changwan@chromium.org

[Changwan Ryu, 2016-09-07 04:14:39]

https://codereview.chromium.org/2073863003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/editing/InputMethodController.cpp (right):

https://codereview.chromium.org/2073863003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/editing/InputMethodController.cpp:320: bool
backspacing = text.length() > 0 && text == composing.left(text.length());
FYI, this workaround is not going to work for Korean characters (and probably
many more). 

One possible Hangul composition sequence is as follows:
가나다라 -> 가나다람 -> 가나다라마 -> 가나다라맙 -> 가나다라마바

Hangul keyboards consider a consonant to be an ending consonant of the current
character until they see a vowel. And if a vowel follows, the consonant becomes
a starting consonant of a new character.

This is not appending nor backspacing in this case.

Can we extend the logic to actually check for the maximal leftmost (I mean
firstmost) characters?

[aelias_OOO_until_Jul13, 2016-09-07 05:11:49]

https://codereview.chromium.org/2073863003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/editing/InputMethodController.cpp (right):

https://codereview.chromium.org/2073863003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/editing/InputMethodController.cpp:320: bool
backspacing = text.length() > 0 && text == composing.left(text.length());
On 2016/09/07 at 04:14:39, Changwan Ryu wrote:
> Can we extend the logic to actually check for the maximal leftmost (I mean
firstmost) characters?

OK.  It looks like I can just use std::distance and std::mismatch for this
(http://codereview.stackexchange.com/questions/104477/fastest-c-code-to-get-co...
)

[aelias_OOO_until_Jul13, 2016-09-28 23:59:16]

For the record, closed this because yabinh@ is polishing this up for landing in
https://codereview.chromium.org/2372493002/