Allow RenderObject::renderName() to be called before style is set

Sometimes we may want to print renderName() or showRenderTree()
in the first setStyle() during debugging a renderer process.
For now they will crash the debugged renderer process and we must
reload the page and reattach gdb to the new renderer process.

Add a check in RenderBlock, RenderInline and
RenderDeprecatedFlexiblebox's renderName() to allow it to be 
called before style is set.

TEST=RenderBlockTest.RenderNameBeforeSetStyle
TEST=RenderInlineTest.RenderNameBeforeSetStyle

Review URL: https://codereview.chromium.org/621943002

git-svn-id: svn://svn.chromium.org/blink/trunk@183356 bbb929c8-8fbe-4397-9dbb-9b2b20218538