Bug 826602 - Rename nsHTMLCanvasElement to mozilla::dom::HTMLCanvasElement; r=bzbarsky

--HG--
rename : content/html/content/public/nsHTMLCanvasElement.h => content/html/content/public/HTMLCanvasElement.h
rename : content/html/content/src/nsHTMLCanvasElement.cpp => content/html/content/src/HTMLCanvasElement.cpp