Reapply "Refactor type propagation."

lib/compiler/implementation/ssa/tracer.dart

Index: lib/compiler/implementation/ssa/tracer.dart
diff --git a/lib/compiler/implementation/ssa/tracer.dart b/lib/compiler/implementation/ssa/tracer.dart
index b3ebb4628830c1b8e77b601f489d88906ef1bacc..4e453141e73aa97cad12628710b1d17e9c1ffedd 100644
--- a/lib/compiler/implementation/ssa/tracer.dart
+++ b/lib/compiler/implementation/ssa/tracer.dart
@@ -165,7 +165,8 @@ class HInstructionStringifier implements HVisitor<String> {
 
   String temporaryId(HInstruction instruction) {
     String prefix;
-    switch (instruction.type) {
+    HType type = instruction.propagatedType;
+    switch (type) {
       case HType.MUTABLE_ARRAY: prefix = 'a'; break;
       case HType.READABLE_ARRAY: prefix = 'roa'; break;
       case HType.BOOLEAN: prefix = 'b'; break;
@@ -402,7 +403,7 @@ class HInstructionStringifier implements HVisitor<String> {
 
   String visitTypeGuard(HTypeGuard node) {
     String type;
-    switch (node.type) {
+    switch (node.propagatedType) {
       case HType.MUTABLE_ARRAY: type = "mutable_array"; break;
       case HType.READABLE_ARRAY: type = "readable_array"; break;
       case HType.BOOLEAN: type = "bool"; break;