Revert 159975 "Update the first letter when the first line is ch..."

Causing use-after-frees on CLusterFuzz.

> Update the first letter when the first line is changed by adding a new text at its start.
> 
> CSS first-letter property does not work properly when the first letter is changed
> by DOM scripting. This patch allows us to update the first letter and remaining text when the
> first letter is changed.
> 
> The original patch was reverted due to the bad cast regression on ClusterFuzz.
> https://codereview.chromium.org/25713009/
> 
> BUG=92797
> TEST=fast/css/first-letter-block-change.html
> 
> Review URL: https://codereview.chromium.org/25647003

TBR=joone.hur@intel.com

Review URL: https://codereview.chromium.org/49943002

git-svn-id: svn://svn.chromium.org/blink/trunk@160758 bbb929c8-8fbe-4397-9dbb-9b2b20218538