Oilpan: Don't use guard pages in NaCl

Source/platform/heap/PageMemory.h

 // Copyright 2015 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 PageMemory_h
 #define PageMemory_h
 
+#include "platform/heap/Heap.h"
 #include "wtf/Assertions.h"
 #include "wtf/PageAllocator.h"
 
 #if OS(POSIX)
 #include <sys/mman.h>
 #include <unistd.h>
 #endif
 
 namespace blink {
 
@@ skipping 178 matching lines @@
     }
 
     void markUnused() { m_reserved->markPageUnused(writableStart()); }
 
     PageMemoryRegion* region() { return m_reserved; }
 
     Address writableStart() { return m_writable.base(); }
 
     static PageMemory* setupPageMemoryInRegion(PageMemoryRegion* region, size_t pageOffset, size_t payloadSize)
     {
         // Setup the payload one OS page into the page memory. The

[sof, 2015/08/16 16:41:56]

nit: could you adjust the comment a bit to reflect what will now happen?

         // first os page is the guard page.
-        Address payloadAddress = region->base() + pageOffset + WTF::kSystemPageSize;
+        Address payloadAddress = region->base() + pageOffset + blinkGuardPageSize;
         return new PageMemory(region, MemoryRegion(payloadAddress, payloadSize));
     }
 
     // Allocate a virtual address space for one blink page with the
     // following layout:
     //
     //    [ guard os page | ... payload ... | guard os page ]
     //    ^---{ aligned to blink page size }
     //
     // The returned page memory region will be zeroed.
     //
     static PageMemory* allocate(size_t payloadSize)
     {
         ASSERT(payloadSize > 0);
 
         // Virtual memory allocation routines operate in OS page sizes.
         // Round up the requested size to nearest os page size.
         payloadSize = roundToOsPageSize(payloadSize);
 
         // Overallocate by 2 times OS page size to have space for a
         // guard page at the beginning and end of blink heap page.
-        size_t allocationSize = payloadSize + 2 * WTF::kSystemPageSize;
+        size_t allocationSize = payloadSize + 2 * blinkGuardPageSize;
         PageMemoryRegion* pageMemoryRegion = PageMemoryRegion::allocateLargePage(allocationSize);
         PageMemory* storage = setupPageMemoryInRegion(pageMemoryRegion, 0, payloadSize);
         RELEASE_ASSERT(storage->commit());
         return storage;
     }
 
 private:
     PageMemory(PageMemoryRegion* reserved, const MemoryRegion& writable)
         : m_reserved(reserved)
         , m_writable(writable)
     {
         ASSERT(reserved->contains(writable));
 
         // Register the writable area of the memory as part of the LSan root set.
         // Only the writable area is mapped and can contain C++ objects.  Those
         // C++ objects can contain pointers to objects outside of the heap and
         // should therefore be part of the LSan root set.
         __lsan_register_root_region(m_writable.base(), m_writable.size());
     }
 
 
     PageMemoryRegion* m_reserved;
     MemoryRegion m_writable;
 };
 
 } // namespace blink
 
 #endif