Bug 837520 - Part 1: Rename nsHTMLBRElement to mozilla::dom::HTMLBRElement; r=bzbarsky

--HG--
rename : content/html/content/src/nsHTMLBRElement.cpp => content/html/content/src/HTMLBRElement.cpp
rename : content/html/content/src/nsHTMLBRElement.cpp => content/html/content/src/HTMLBRElement.h
Bug 837520 - Part 2: Move HTMLBRElement to Web IDL bindings; r=bzbarsky