Refactoring DrawLooper so that it can apply shadow effects as skia image filters

LayoutTests/platform/mac/virtual/gpu/fast/canvas/canvas-draw-canvas-on-canvas-shadow-expected.txt

Index: LayoutTests/platform/mac/virtual/gpu/fast/canvas/canvas-draw-canvas-on-canvas-shadow-expected.txt
diff --git a/LayoutTests/platform/mac/virtual/gpu/fast/canvas/canvas-draw-canvas-on-canvas-shadow-expected.txt b/LayoutTests/platform/mac/virtual/gpu/fast/canvas/canvas-draw-canvas-on-canvas-shadow-expected.txt
deleted file mode 100644
index 4711ea73060d9d4229e15c7784e9c6c2246bcca4..0000000000000000000000000000000000000000
--- a/LayoutTests/platform/mac/virtual/gpu/fast/canvas/canvas-draw-canvas-on-canvas-shadow-expected.txt
+++ /dev/null
@@ -1,57 +0,0 @@
-Ensure correct behavior when drawing a canvas on a canvas with shadows. A blue and red checkered pattern should be displayed.
-
-On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
-
-
-PASS d[0] is 255
-PASS d[1] is 0
-PASS d[2] is 0
-PASS d[3] is 255
-PASS d[0] is 255
-PASS d[1] is 0
-PASS d[2] is 0
-PASS d[3] is 255
-PASS d[0] is 255
-PASS d[1] is 0
-PASS d[2] is 0
-PASS d[3] is 255
-PASS d[0] is 255
-PASS d[1] is 0
-PASS d[2] is 0
-PASS d[3] is around 127
-PASS d[0] is 255
-PASS d[1] is 0
-PASS d[2] is 0
-PASS d[3] is around 127
-PASS d[0] is 255
-PASS d[1] is 0
-PASS d[2] is 0
-PASS d[3] is around 127
-FAIL d[0] should be 255. Was 0.
-PASS d[1] is 0
-PASS d[2] is 0
-FAIL d[3] is not around 100 (actual: 0)
-FAIL d[0] should be 255. Was 0.
-PASS d[1] is 0
-PASS d[2] is 0
-FAIL d[3] is not around 100 (actual: 0)
-FAIL d[0] should be 255. Was 0.
-PASS d[1] is 0
-PASS d[2] is 0
-FAIL d[3] is not around 100 (actual: 0)
-FAIL d[0] should be 255. Was 0.
-PASS d[1] is 0
-PASS d[2] is 0
-FAIL d[3] is not around 50 (actual: 0)
-FAIL d[0] should be 255. Was 0.
-PASS d[1] is 0
-PASS d[2] is 0
-FAIL d[3] is not around 50 (actual: 0)
-FAIL d[0] should be 255. Was 0.
-PASS d[1] is 0
-PASS d[2] is 0
-FAIL d[3] is not around 50 (actual: 0)
-PASS successfullyParsed is true
-
-TEST COMPLETE
-