dart2js cps: Avoid deep recursion using trampolines and basic blocks.

pkg/compiler/lib/src/cps_ir/mutable_ssa.dart

Index: pkg/compiler/lib/src/cps_ir/mutable_ssa.dart
diff --git a/pkg/compiler/lib/src/cps_ir/mutable_ssa.dart b/pkg/compiler/lib/src/cps_ir/mutable_ssa.dart
index c561e818f7495c11ae7dab409237b4640a42ae17..d01c3f5e33e2ce48f9ef4e3227ff766bf84a9308 100644
--- a/pkg/compiler/lib/src/cps_ir/mutable_ssa.dart
+++ b/pkg/compiler/lib/src/cps_ir/mutable_ssa.dart
@@ -26,11 +26,12 @@ class MutableVariablePreanalysis extends RecursiveVisitor {
   /// its declaration.
   Set<MutableVariable> hasAssignmentInTry = new Set<MutableVariable>();
 
-  void visitLetHandler(LetHandler node) {
+  @override
+  Expression traverseLetHandler(LetHandler node) {
+    push(node.handler);
     ++currentDepth;
-    visit(node.body);
-    --currentDepth;
-    visit(node.handler);
+    pushAction(() => --currentDepth);
+    return node.body;
   }
 
   void processLetMutable(LetMutable node) {