[oilpan]: optimize the way we allocate persistent handles in wrappers.

Source/platform/heap/Handle.cpp

Index: Source/platform/heap/Handle.cpp
diff --git a/Source/platform/heap/Handle.cpp b/Source/platform/heap/Handle.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..a266ae72dce866d8fdbdc7d2641546e3da7ba35c
--- /dev/null
+++ b/Source/platform/heap/Handle.cpp
@@ -0,0 +1,74 @@
+// Copyright 2014 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.
+
+#include "config.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+bool WrapperPersistentRegion::removeIfNotLast(WrapperPersistentRegion** headPtr)
+{
+    ASSERT(!m_count);
+    // We are the last region in the list if both the region's m_prev and
+    // m_next are 0.
+    if (!m_prev && !m_next)
+        return false;
+    if (m_prev) {
+        m_prev->m_next = m_next;
+    } else {
+        ASSERT(*headPtr == this);
+        *headPtr = m_next;
+    }
+    if (m_next)
+        m_next->m_prev = m_prev;
+    m_prev = 0;
+    m_next = 0;
+    return true;
+}
+
+void WrapperPersistentRegion::insertHead(WrapperPersistentRegion** headPtr, WrapperPersistentRegion* newHead)
+{
+    ASSERT(headPtr);
+    WrapperPersistentRegion* oldHead = *headPtr;
+    if (oldHead) {
+        ASSERT(!oldHead->m_prev);
+        oldHead->m_prev = newHead;
+    }
+    newHead->m_prev = 0;
+    newHead->m_next = oldHead;
+    *headPtr = newHead;
+}
+
+WrapperPersistentRegion* WrapperPersistentRegion::removeHead(WrapperPersistentRegion** headPtr)
+{
+    // We only call this if there is at least one element in the list.
+    ASSERT(headPtr && *headPtr);
+    WrapperPersistentRegion* oldHead = *headPtr;
+    ASSERT(!oldHead->m_prev);
+    *headPtr = oldHead->m_next;
+    oldHead->m_next = 0;
+    ASSERT(!(*headPtr) || (*headPtr)->m_prev == oldHead);
+    if (*headPtr)
+        (*headPtr)->m_prev = 0;
+    return oldHead;
+}
+
+void* WrapperPersistentRegion::outOfLineAllocate(ThreadState* state, WrapperPersistentRegion* head)
+{
+    void* persistent = 0;
+    // The caller has already tried allocating in the passed-in region, start
+    // from the next.
+    for (WrapperPersistentRegion* current = head->m_next; current; current = current->m_next) {
+        persistent = current->allocate();
+        if (persistent)
+            return persistent;
+    }
+    ASSERT(!persistent);
+    WrapperPersistentRegion* newRegion = state->addWrapperPersistentRegion();
+    persistent = newRegion->allocate();
+    ASSERT(persistent);
+    return persistent;
+}
+
+}