Restore only the collapsed leading space when copy text

When we need to restore the trailing space of a line and the
leading space of the next line together for copy operation,
we don't have to restore the trailing space in the first line.
Example: <div style="width: 2em;"><b><i>foo </i></b> bar</div>

BUG=318925
TEST=TextIteratorTest.PreserveOnlyLeadingSpace

Review-Url: https://codereview.chromium.org/2336043006
Cr-Commit-Position: refs/heads/master@{#421133}
2 files changed