background-color and text-decoration are not preserved when merging paragraphs

In mergeInlineAndImplicitStyleOfElement(), the element styles are retrieved.
If they contain either background-color or text-decoration they will be removed
by removeNonEditingProperties() due to copyEditingProperties() implicit
OnlyInheritableEditingProperties parameter.

WebKit merge from r151772 and r152286

BUG=268922

Review URL: https://chromiumcodereview.appspot.com/22353004

git-svn-id: svn://svn.chromium.org/blink/trunk@155705 bbb929c8-8fbe-4397-9dbb-9b2b20218538