After a dynamic call, refine the receiver type by looking at the potential targets of that call.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/tracer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/tracer.dart	(revision 22031)
+++ sdk/lib/_internal/compiler/implementation/ssa/tracer.dart	(working copy)
@@ -83,10 +83,12 @@
       int uses = instruction.usedBy.length;
       String changes = instruction.hasSideEffects() ? '!' : ' ';
       String depends = instruction.dependsOnSomething() ? '?' : '';
+      String usesGvn = instruction.useGvn() ? 'G' : '';
       addIndent();
       String temporaryId = stringifier.temporaryId(instruction);
       String instructionString = stringifier.visit(instruction);
-      add("$bci $uses $temporaryId $instructionString $changes $depends <|@\n");
+      add("$bci $uses $temporaryId $instructionString "
+          "$changes $depends $usesGvn <|@\n");
     }
   }