Also implement SkGPipeCanvas::drawBitmapMatrix, and
create a GM to make sure it works properly.
Use a flag instead of writing a bool for determining whether
drawBitmap_ has a paint and whether drawBitmapRect has a source
rectangle.
BUG=
TEST=drawbitmapmatrix GM
Review URL: https://codereview.appspot.com/6450053
git-svn-id: http://skia.googlecode.com/svn/trunk@4828 2bbb7eff-a529-9590-31e7-b0007b416f81
