Speed up the Dart_IsBlah functions by checking the class index. This

vm/dart_api_impl.h

 // Copyright (c) 2011, 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 VM_DART_API_IMPL_H_
 #define VM_DART_API_IMPL_H_
 
 #include "vm/allocation.h"
 #include "vm/object.h"
 
@@ skipping 105 matching lines @@
     RawObject* raw = *(reinterpret_cast<RawObject**>(handle));
     return !raw->IsHeapObject();
   }
 
   // Returns the value of a Smi.
   static intptr_t SmiValue(Dart_Handle handle) {
     uword value = *(reinterpret_cast<uword*>(handle));
     return Smi::ValueFromRaw(value);
   }
 
+  static intptr_t ClassIndex(Dart_Handle handle) {
+    RawObject* raw = *(reinterpret_cast<RawObject**>(handle));
+    if (!raw->IsHeapObject()) {
+      return kSmi;
+    }
+    return raw->GetClassIndex();
+  }
+
   // Generates a handle used to designate an error return.
   static Dart_Handle NewError(const char* format, ...);
 
   // Gets a handle to Null.
   static Dart_Handle Null(Isolate* isolate);
 
   // Gets a handle to True.
   static Dart_Handle True(Isolate* isolate);
 
   // Gets a handle to False
@@ skipping 29 matching lines @@
   }
  private:
   Isolate* saved_isolate_;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateSaver);
 };
 
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_