Convert some pixel tests in fast/canvas into ref tests.

LayoutTests/fast/canvas/canvas-zoom-expected.txt

Index: LayoutTests/fast/canvas/canvas-zoom-expected.txt
diff --git a/LayoutTests/fast/canvas/canvas-zoom-expected.txt b/LayoutTests/fast/canvas/canvas-zoom-expected.txt
deleted file mode 100644
index 288458d5994b51db82ab875c6e12930c6cfa1158..0000000000000000000000000000000000000000
--- a/LayoutTests/fast/canvas/canvas-zoom-expected.txt
+++ /dev/null
@@ -1,22 +0,0 @@
-layer at (0,0) size 800x600
-  RenderView at (0,0) size 800x600
-layer at (0,0) size 800x600
-  RenderBlock {HTML} at (0,0) size 800x600
-    RenderBody {BODY} at (8,8) size 784x584
-      RenderBlock {P} at (0,0) size 784x18
-        RenderText {#text} at (0,0) size 624x18
-          text run at (0,0) width 624: "These should be four green hollow boxes with dimensions 600x300, 100x300, 600x100, 100x100."
-      RenderBlock (anonymous) at (0,34) size 784x420
-        RenderHTMLCanvas {CANVAS} at (0,0) size 606x306 [border: (3px solid #008000)]
-        RenderText {#text} at (606,292) size 4x18
-          text run at (606,292) width 4: " "
-        RenderText {#text} at (0,0) size 0x0
-        RenderHTMLCanvas {CANVAS} at (610,0) size 106x306 [border: (3px solid #008000)]
-        RenderText {#text} at (0,0) size 0x0
-        RenderText {#text} at (0,0) size 0x0
-        RenderHTMLCanvas {CANVAS} at (0,310) size 606x106 [border: (3px solid #008000)]
-        RenderText {#text} at (606,402) size 4x18
-          text run at (606,402) width 4: " "
-        RenderText {#text} at (0,0) size 0x0
-        RenderHTMLCanvas {CANVAS} at (610,310) size 106x106 [border: (3px solid #008000)]
-        RenderText {#text} at (0,0) size 0x0