When canonicalize instances check if all fields are canonical. If a field is a non-canonical number…

runtime/vm/dart_entry.cc

Index: runtime/vm/dart_entry.cc
===================================================================
--- runtime/vm/dart_entry.cc	(revision 23933)
+++ runtime/vm/dart_entry.cc	(working copy)
@@ -240,7 +240,8 @@
 
   // Share the immutable descriptor when possible by canonicalizing it.
   descriptor.MakeImmutable();
-  descriptor ^= descriptor.Canonicalize();
+  descriptor ^= descriptor.CheckAndCanonicalize(NULL);
+  ASSERT(!descriptor.IsNull());
   return descriptor.raw();
 }
 
@@ -275,8 +276,9 @@
   // Share the immutable descriptor when possible by canonicalizing it.
   descriptor.MakeImmutable();
   if (canonicalize) {
-    descriptor ^= descriptor.Canonicalize();
+    descriptor ^= descriptor.CheckAndCanonicalize(NULL);
   }
+  ASSERT(!descriptor.IsNull());
   return descriptor.raw();
 }