Fix duplication of the megamorphic miss function when running a JIT app snapshot.

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
diff --git a/runtime/vm/dart.cc b/runtime/vm/dart.cc
index 2f9e6d7b694a6bb8693440f72a489ccac5f875de..01dce70fe036c1fc65f080963af224707d4ede6a 100644
--- a/runtime/vm/dart.cc
+++ b/runtime/vm/dart.cc
@@ -583,7 +583,7 @@ RawError* Dart::InitializeIsolate(const uint8_t* snapshot_buffer,
 #if !defined(DART_PRECOMPILED_RUNTIME)
   // When running precompiled, the megamorphic miss function/code comes from the
   // snapshot.

[siva, 2017/01/05 23:10:47]

The comment here also probably needs an update
(precompiled and running from an application snapshot) ?

[rmacnak, 2017/01/05 23:32:44]

Done.

-  if (!Snapshot::IncludesCode(Dart::snapshot_kind())) {
+  if (I->object_store()->megamorphic_miss_function() == Function::null()) {
     MegamorphicCacheTable::InitMissHandler(I);
   }
 #endif

[siva, 2017/01/05 23:10:47]

Should this be set up as

#if defined(DART_PRECOMPILED_RUNTIME)
   // When running precompiled, the megamorphic mi.....
   ASSERT(I->object_store()->megamorphic_miss_function() != Function::null());
#else
   // When running from an application snapshot ....
   if (I->object_store()->megamorphic_miss_function() == Function...) {
      ....
    }
#endif  // defined(DART_PRECOMPILED_RUNTIME)

[rmacnak, 2017/01/05 23:32:44]

Done.