IDL: Null values should be converted for non-nullable dictionary members

LayoutTests/fast/canvas/canvas-hit-regions-basic-test.html

Index: LayoutTests/fast/canvas/canvas-hit-regions-basic-test.html
diff --git a/LayoutTests/fast/canvas/canvas-hit-regions-basic-test.html b/LayoutTests/fast/canvas/canvas-hit-regions-basic-test.html
index 4d8179ed4d3091345ec58743d56b5aaf4449e954..dbae6b990b691fdfd83d6b34c394ecd79f83aee4 100644
--- a/LayoutTests/fast/canvas/canvas-hit-regions-basic-test.html
+++ b/LayoutTests/fast/canvas/canvas-hit-regions-basic-test.html
@@ -77,6 +77,8 @@
   debug("NotSupportedError exception tests");
   shouldThrow("context.addHitRegion()");
   shouldThrow("context.addHitRegion({ id : '' })");
+  // This test fails. ToString(null) becomes "null", and it seems that "null" is a valid value for id.
+  // (e.g. <div id="null"></div>)
   shouldThrow("context.addHitRegion({ id : null })");
   shouldThrow("context.addHitRegion({ id : undefined })");
   shouldThrow("context.addHitRegion({ control : {} })");