Make Oilpan's Persistent handle work with const types.

third_party/WebKit/Source/platform/heap/Persistent.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef Persistent_h
 #define Persistent_h
 
 #include "platform/heap/Heap.h"
 #include "platform/heap/Member.h"
 #include "platform/heap/PersistentNode.h"
@@ skipping 149 matching lines @@
       ThreadState::current()->registerStaticPersistentNode(m_persistentNode,
                                                            nullptr);
       LEAK_SANITIZER_IGNORE_OBJECT(this);
     }
     return this;
   }
 
  protected:
   NO_SANITIZE_ADDRESS
   T* atomicGet() {
-    return reinterpret_cast<T*>(
-        acquireLoad(reinterpret_cast<void* volatile*>(&m_raw)));
+    return reinterpret_cast<T*>(acquireLoad(reinterpret_cast<void* volatile*>(
+        const_cast<typename std::remove_const<T>::type**>(&m_raw))));
   }
 
  private:
   NO_SANITIZE_ADDRESS
   void assign(T* ptr) {
-    if (crossThreadnessConfiguration == CrossThreadPersistentConfiguration)
-      releaseStore(reinterpret_cast<void* volatile*>(&m_raw), ptr);
-    else
+    if (crossThreadnessConfiguration == CrossThreadPersistentConfiguration) {
+      releaseStore(
+          reinterpret_cast<void* volatile*>(
+              const_cast<typename std::remove_const<T>::type**>(&m_raw)),
+          const_cast<typename std::remove_const<T>::type*>(ptr));
+    } else {
       m_raw = ptr;
+    }
     checkPointer();
     if (m_raw) {
       if (!m_persistentNode)
         initialize();
       return;
     }
     uninitialize();
   }
 
   template <typename VisitorDispatcher>
@@ skipping 625 matching lines @@
   static blink::CrossThreadPersistent<T> Unwrap(
       const blink::CrossThreadWeakPersistent<T>& wrapped) {
     blink::CrossThreadPersistentRegion::LockScope persistentLock(
         blink::ProcessHeap::crossThreadPersistentRegion());
     return blink::CrossThreadPersistent<T>(wrapped.get());
   }
 };
 }
 
 #endif  // Persistent_h