When "end of line" is an isolated element, InlineIterator::increment is wrongly
moving the iterator to the next object.
This patch fixes the behavior verifying if endOfLine is the current isolated object 
or a child of it.
Now the worst case scenario for Inline::increment happens when endOfLine is the isolated element.

BUG=326860

Review URL: https://codereview.chromium.org/103823005

git-svn-id: svn://svn.chromium.org/blink/trunk@164123 bbb929c8-8fbe-4397-9dbb-9b2b20218538