Tests: 
Copying and pasting content inside of a PRE tag. This test was created after fixing 3918056.
Expected Results: 
The PRE tag and the formatting of the text inside of the PRE should be maintained. Should see this content in the red box below:
foo
bar
foo
bar
execCutCommand: <div id="test" class="editing"> <pre><br></pre> </div>
execPasteCommand: <div id="test" class="editing"> <pre>foo bar</pre> </div>
