Adding the 'filter' context attribute to 2D canvas

LayoutTests/fast/canvas/canvas-filter-svg-inline.html

Index: LayoutTests/fast/canvas/canvas-filter-svg-inline.html
diff --git a/LayoutTests/fast/canvas/canvas-filter-svg-inline.html b/LayoutTests/fast/canvas/canvas-filter-svg-inline.html
new file mode 100644
index 0000000000000000000000000000000000000000..d63f073183f681fb70dbff72d441d787ad1269b5
--- /dev/null
+++ b/LayoutTests/fast/canvas/canvas-filter-svg-inline.html
@@ -0,0 +1,22 @@
+<svg style="display: block; width: 0; height: 0">
+  <defs>
+    <filter id="drop-shadow">
+      <fegaussianblur in="SourceAlpha" stdDeviation="0"></fegaussianblur>

[Stephen White, 2015/06/25 18:30:27]

Nit: stddev = 0 => perhaps this node is not needed?

+      <feoffset dx="0" dy="10" result="offsetblur"></feoffset>
+      <feflood flood-color="rgba(0,0,0,1)"></feflood>
+      <fecomposite in2="offsetblur" operator="in"></fecomposite>
+      <femerge>
+        <femergenode></femergenode>
+        <femergenode in="SourceGraphic"></femergenode>
+      </femerge>
+    </filter>
+  </defs>
+</svg>
+<canvas id="canvas" width="100" height="100"></canvas>
+<script>
+var canvas = document.getElementById('canvas');
+var ctx = canvas.getContext('2d');
+ctx.filter = 'url(#drop-shadow)';
+ctx.fillStyle = '#0f0';
+ctx.fillRect(25, 25, 50, 40);
+</script>