Adding the 'filter' context attribute to 2D canvas

LayoutTests/fast/canvas/canvas-filter-shadow.html

Index: LayoutTests/fast/canvas/canvas-filter-shadow.html
diff --git a/LayoutTests/fast/canvas/canvas-filter-shadow.html b/LayoutTests/fast/canvas/canvas-filter-shadow.html
new file mode 100644
index 0000000000000000000000000000000000000000..cc1dbaa17265723d6d65ed5fc088636fe8895046
--- /dev/null
+++ b/LayoutTests/fast/canvas/canvas-filter-shadow.html
@@ -0,0 +1,10 @@
+<canvas id="canvas" width="100" height="100"></canvas>
+<script>
+var canvas = document.getElementById('canvas');
+var ctx = canvas.getContext('2d');
+ctx.fillStyle = '#0f0';
+ctx.filter = 'drop-shadow(0px 10px black)';
+ctx.shadowOffsetX = 10;
+ctx.shadowColor = '#ccc';
+ctx.fillRect(20, 25, 50, 40);
+</script>