Treat received Path as a const.

Skia internally will either create a new Path object in a call
to 'transform' or can do it inplace if the destination pointer
is the same as the source.

By copying the Path object on start, we can treat the received
Path as a const reference instead of a pointer and save 2 function
calls to set/restore the fill type.

BUG=236559

Review URL: https://chromiumcodereview.appspot.com/19846006

git-svn-id: svn://svn.chromium.org/blink/trunk@154713 bbb929c8-8fbe-4397-9dbb-9b2b20218538