Bump-pointer allocation when reading snapshot; 10-15% faster isolate creation.

runtime/vm/snapshot.cc

 // 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.
 
 #include "vm/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/exceptions.h"
@@ skipping 811 matching lines @@
   }
   return Class::null();
 }
 
 
 RawObject* SnapshotReader::AllocateUninitialized(intptr_t class_id,
                                                  intptr_t size) {
   ASSERT(isolate()->no_gc_scope_depth() != 0);
   ASSERT(Utils::IsAligned(size, kObjectAlignment));
 
-  uword address = old_space()->TryAllocateDataLocked(size,
-                                                     PageSpace::kForceGrowth);
+  uword address =
+      old_space()->TryAllocateDataBumpLocked(size, PageSpace::kForceGrowth);
   if (address == 0) {
     // Use the preallocated out of memory exception to avoid calling
     // into dart code or allocating any code.
     // We do a longjmp at this point to unwind out of the entire
     // read part and return the error object back.
     const UnhandledException& error = UnhandledException::Handle(
         object_store()->preallocated_unhandled_exception());
     Isolate::Current()->long_jump_base()->Jump(1, error);
   }
 #if defined(DEBUG)
@@ skipping 921 matching lines @@
     NoGCScope no_gc;
     WriteObject(obj.raw());
     UnmarkAll();
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart