add support for custom Java Drawables

This is made possible, by adding a second Canvas implementation which
can be used to render directly to GdkSnapshot objects

For now the only implemented method is drawBitmap(), this is already
enough to make VectorDrawableCompat functional

src/api-impl/android/graphics/drawable/RippleDrawable.java

@@ -1,15 +1,9 @@
 package android.graphics.drawable;
 
 import android.content.res.ColorStateList;
-import android.graphics.Canvas;
 
 public class RippleDrawable extends Drawable {
 
 	public RippleDrawable(ColorStateList colorStateList, Drawable drawable, Drawable drawable2) {}
 
-	@Override
-	public void draw(Canvas canvas) {
-		// TODO Auto-generated method stub
-		throw new UnsupportedOperationException("Unimplemented method 'draw'");
-	}
 }