VM: Support bootstrapping core libraries from Kernel binaries instead of source.

runtime/vm/raw_object.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef RUNTIME_VM_RAW_OBJECT_H_
 #define RUNTIME_VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/atomic.h"
 #include "vm/globals.h"
@@ skipping 717 matching lines @@
   friend class SnapshotReader;
   friend class InstanceSerializationCluster;
   friend class CidRewriteVisitor;
 };
 
 
 class RawUnresolvedClass : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(UnresolvedClass);
 
   RawObject** from() {
-    return reinterpret_cast<RawObject**>(&ptr()->library_prefix_);
+    return reinterpret_cast<RawObject**>(&ptr()->library_or_library_prefix_);
   }
-  RawLibraryPrefix* library_prefix_;  // Library prefix qualifier for the ident.
+  RawObject* library_or_library_prefix_;  // Library or library prefix qualifier

[hausner, 2016/11/09 18:21:36]

I don't see where the CL makes use of this change. Why is it necessary?

[Vyacheslav Egorov (Google), 2016/11/09 18:44:52]

Sorry, I missed this question. 

See kernel_to_il.cc ->
https://codereview.chromium.org/2485993002/diff/60001/runtime/vm/kernel_to_il...

In short we would like to reuse some of the (type) finalization machinery (most
importantly given type like X<T> get a properly expanded list of type
arguments). To reuse this machinery as is we need to be able to create
unresolved types - which requires creating unresolved classes. However to create
unresolved classes we need LibraryPrefix - and we don't have such thing in
Kernel because kernel is completely resolved. 

Hence this change. 

In some sense it's a gross hack - however an alternative seems to be to
duplicate parts of class finalizer - which seems to be a considerably bigger
change. 

[hausner, 2016/11/09 19:07:01]

Ah, I see now. 

+                                          // for the ident.
   RawString* ident_;  // Name of the unresolved identifier.
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->ident_);
   }
   TokenPosition token_pos_;
 };
 
 
 class RawTypeArguments : public RawObject {
  private:
@@ skipping 1736 matching lines @@
   COMPILE_ASSERT(kExternalTypedDataInt8ArrayCid ==
                  kTypedDataInt8ArrayViewCid + 15);
   COMPILE_ASSERT(kByteBufferCid == kExternalTypedDataInt8ArrayCid + 14);
   COMPILE_ASSERT(kNullCid == kByteBufferCid + 1);
   return (kNullCid - kTypedDataInt8ArrayCid);
 }
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_RAW_OBJECT_H_