Resubmit change 6302 after fixing the compiler warning on older GCC compiler versions:

vm/pages.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/pages.h"
 
 #include "platform/assert.h"
 #include "vm/gc_marker.h"
 #include "vm/gc_sweeper.h"
 #include "vm/object.h"
@@ skipping 31 matching lines @@
   uword obj_addr = first_object_start();
   uword end_addr = top();
   while (obj_addr < end_addr) {
     RawObject* raw_obj = RawObject::FromAddr(obj_addr);
     obj_addr += raw_obj->VisitPointers(visitor);
   }
   ASSERT(obj_addr == end_addr);
 }
 
 
+RawObject* HeapPage::FindObject(FindObjectVisitor* visitor) const {
+  uword obj_addr = first_object_start();
+  uword end_addr = top();
+  while (obj_addr < end_addr) {
+    RawObject* raw_obj = RawObject::FromAddr(obj_addr);
+    if (raw_obj->FindObject(visitor)) {
+      return raw_obj;  // Found object, return it.
+    }
+    obj_addr += raw_obj->Size();
+  }
+  ASSERT(obj_addr == end_addr);
+  return Object::null();
+}
+
+
 PageSpace::PageSpace(Heap* heap, intptr_t max_capacity, bool is_executable)
     : freelist_(),
       heap_(heap),
       pages_(NULL),
       pages_tail_(NULL),
       large_pages_(NULL),
       max_capacity_(max_capacity),
       capacity_(0),
       in_use_(0),
       count_(0),
@@ skipping 137 matching lines @@
   }
 
   page = large_pages_;
   while (page != NULL) {
     page->VisitObjectPointers(visitor);
     page = page->next();
   }
 }
 
 
+RawObject* PageSpace::FindObject(FindObjectVisitor* visitor) const {
+  ASSERT(Isolate::Current()->no_gc_scope_depth() != 0);
+  HeapPage* page = pages_;
+  while (page != NULL) {
+    RawObject* obj = page->FindObject(visitor);
+    if (obj != Object::null()) {
+      return obj;
+    }
+    page = page->next();
+  }
+
+  page = large_pages_;
+  while (page != NULL) {
+    RawObject* obj = page->FindObject(visitor);
+    if (obj != Object::null()) {
+      return obj;
+    }
+    page = page->next();
+  }
+  return Object::null();
+}
+
+
 void PageSpace::MarkSweep(bool invoke_api_callbacks) {
   // MarkSweep is not reentrant. Make sure that is the case.
   ASSERT(!sweeping_);
   sweeping_ = true;
   Isolate* isolate = Isolate::Current();
   NoHandleScope no_handles(isolate);
 
   if (FLAG_verify_before_gc) {
     OS::PrintErr("Verifying before MarkSweep... ");
     heap_->Verify();
@@ skipping 54 matching lines @@
     OS::PrintErr(" done.\n");
   }
 
   count_++;
   // Done, reset the marker.
   ASSERT(sweeping_);
   sweeping_ = false;
 }
 
 }  // namespace dart