This adds a mechanism to invalidate code that was generated in the background. The invalidation can…

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index d2f3a499143ca7a949a0cbaa43b89384da360770..0a3b9ec1d2e5881eede608462431e4c0d2b11d92 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -2890,6 +2890,10 @@ class CHACodeArray : public WeakCodeReferences {
     }
   }
 
+  virtual void IncrementInvalidationGen() {
+    Isolate::Current()->IncrCHAInvalidationGen();
+  }
+
  private:
   const Class& cls_;
   DISALLOW_COPY_AND_ASSIGN(CHACodeArray);
@@ -7774,6 +7778,10 @@ class FieldDependentArray : public WeakCodeReferences {
     }
   }
 
+  virtual void IncrementInvalidationGen() {
+    Isolate::Current()->IncrFieldInvalidationGen();
+  }
+
  private:
   const Field& field_;
   DISALLOW_COPY_AND_ASSIGN(FieldDependentArray);
@@ -10815,6 +10823,10 @@ class PrefixDependentArray : public WeakCodeReferences {
     }
   }
 
+  virtual void IncrementInvalidationGen() {
+    Isolate::Current()->IncrPrefixInvalidationGen();
+  }
+
  private:
   const LibraryPrefix& prefix_;
   DISALLOW_COPY_AND_ASSIGN(PrefixDependentArray);
@@ -17051,9 +17063,9 @@ void Number::PrintJSONImpl(JSONStream* stream, bool ref) const {
 
 
 const char* Integer::ToCString() const {
-  // Integer is an interface. No instances of Integer should exist.
-  UNREACHABLE();
-  return "Integer";
+  // Integer is an interface. No instances of Integer should exist except null.
+  ASSERT(IsNull());
+  return "NULL Integer";
 }