Optimize num::~/, num::>> and num::<< for some cases.

sdk/lib/_internal/compiler/implementation/ssa/codegen.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/codegen.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/codegen.dart	(revision 31017)
+++ sdk/lib/_internal/compiler/implementation/ssa/codegen.dart	(working copy)
@@ -1249,6 +1249,16 @@
   visitShiftLeft(HShiftLeft node)   => visitBitInvokeBinary(node, '<<');
   visitShiftRight(HShiftRight node) => visitBitInvokeBinary(node, '>>>');
 
+  visitTruncatingDivide(HTruncatingDivide node) {
+    assert(node.left.isUInt31(compiler));
+    assert(node.right.isPositiveInteger(compiler));
+    use(node.left);
+    js.Expression jsLeft = pop();
+    use(node.right);
+    push(new js.Binary('/', jsLeft, pop()), node);
+    push(new js.Binary('|', pop(), new js.LiteralNumber("0")), node);
+  }
+
   visitNegate(HNegate node)         => visitInvokeUnary(node, '-');
 
   visitLess(HLess node)                 => visitRelational(node, '<');