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

git-svn-id: svn://svn.chromium.org/blink/trunk@159975 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make WebPrivateOwnPtr inherited from WebNonCopyable

Make WebPrivateOwnPtr inherited from WebNonCopyable rather than declare private copy constructor and assignment operator inside WebPrivateOwnPtr.
Another rational is that the assignment operator was declared wrongly in WebPrivateOwnPtr.

Review URL: https://codereview.chromium.org/26512004

git-svn-id: svn://svn.chromium.org/blink/trunk@159976 bbb929c8-8fbe-4397-9dbb-9b2b20218538