Shrink some fields and add some bounds checks.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index f571979ac5c49fb1421365a4ad4aab9f5933f812..0a26c097f1cee4daef97b717de149bc90c43b030 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -613,11 +613,11 @@ class RawClass : public RawObject {
   }
 
   cpp_vtable handle_vtable_;
-  int32_t id_;  // Class Id, also index in the class table.
   int32_t token_pos_;
   int32_t instance_size_in_words_;  // Size if fixed len or 0 if variable len.
   int32_t type_arguments_field_offset_in_words_;  // Offset of type args fld.
   int32_t next_field_offset_in_words_;  // Offset of the next instance field.
+  uint16_t id_;  // Class Id, also index in the class table.

[rmacnak, 2015/06/02 21:04:11]

Limited by object header

   int16_t num_type_arguments_;  // Number of type arguments in flatten vector.
   int16_t num_own_type_arguments_;  // Number of non-overlapping type arguments.
   uint16_t num_native_fields_;  // Number of native fields in class.
@@ -915,15 +915,15 @@ class RawLibrary : public RawObject {
     return reinterpret_cast<RawObject**>(&ptr()->load_error_);
   }
 
-  int32_t index_;               // Library id number.
-  int32_t num_imports_;         // Number of entries in imports_.
-  int32_t num_anonymous_;       // Number of entries in anonymous_classes_.
   Dart_NativeEntryResolver native_entry_resolver_;  // Resolves natives.
   Dart_NativeEntrySymbol native_entry_symbol_resolver_;
+  uint16_t index_;              // Library id number.

[rmacnak, 2015/06/02 21:04:11]

Limited by number of classes

+  uint16_t num_imports_;        // Number of entries in imports_.
+  uint16_t num_anonymous_;      // Number of entries in anonymous_classes_.
+  int8_t load_state_;           // Of type LibraryState.
   bool corelib_imported_;
   bool is_dart_scheme_;
-  bool debuggable_;              // True if debugger can stop in library.
-  int8_t load_state_;            // Of type LibraryState.
+  bool debuggable_;             // True if debugger can stop in library.
 
   friend class Isolate;
 };
@@ -1399,7 +1399,7 @@ class RawLibraryPrefix : public RawInstance {
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->dependent_code_);
   }
-  int32_t num_imports_;          // Number of library entries in libraries_.
+  int16_t num_imports_;          // Number of library entries in libraries_.
   bool is_deferred_load_;
   bool is_loaded_;
 };
@@ -1465,8 +1465,8 @@ class RawTypeParameter : public RawAbstractType {
   RawString* name_;
   RawAbstractType* bound_;  // ObjectType if no explicit bound specified.
   RawObject** to() { return reinterpret_cast<RawObject**>(&ptr()->bound_); }
-  int32_t index_;
   int32_t token_pos_;
+  int16_t index_;

[rmacnak, 2015/06/02 21:04:11]

Limited by num_type_arguments_ in RawClass

   int8_t type_state_;
 };