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

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
index 63d1a05355ba8a9d7381f3f0d3c9f9e3193ecd3d..f07a03005ffdc30b24750bc064f0190201e66c81 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
@@ -92,7 +92,9 @@ class BlockCollector extends StatementVisitor {
 
   visitBreak(Break node) {
     _addStatement(node);
-    blocks.last.addEdgeTo(breakTargets[node.target]);
+    if (breakTargets.containsKey(node.target)) {
+      blocks.last.addEdgeTo(breakTargets[node.target]);
+    }
   }
 
   visitContinue(Continue node) {
@@ -274,7 +276,9 @@ class TreeTracer extends TracerUtil with StatementVisitor {
   }
 
   visitBreak(Break node) {
-    printStatement(null, "break ${collector.breakTargets[node.target].name}");
+    Block block = collector.breakTargets[node.target];
+    String name = block != null ? block.name : '<missing label>';
+    printStatement(null, "break $name");
   }
 
   visitContinue(Continue node) {