Use a bitmap to record PageMemoryRegion usage.

third_party/WebKit/Source/platform/heap/PageMemory.cpp

Index: third_party/WebKit/Source/platform/heap/PageMemory.cpp
diff --git a/third_party/WebKit/Source/platform/heap/PageMemory.cpp b/third_party/WebKit/Source/platform/heap/PageMemory.cpp
index 5efe1fcede7eb3036afbf20179a5dcfb76e7911d..9ed5666386fb677593f48f6db6f8b24707730876 100644
--- a/third_party/WebKit/Source/platform/heap/PageMemory.cpp
+++ b/third_party/WebKit/Source/platform/heap/PageMemory.cpp
@@ -31,11 +31,11 @@ void MemoryRegion::decommit()
 PageMemoryRegion::PageMemoryRegion(Address base, size_t size, unsigned numPages)
     : MemoryRegion(base, size)
     , m_isLargePage(numPages == 1)
+    , m_inUseBitmap(0)
     , m_numPages(numPages)
 {
+    static_assert(blinkPagesPerRegion < 8 * sizeof(unsigned), "PageMemoryRegion's in-use bitmap must fit within a word.");
     Heap::addPageMemoryRegion(this);
-    for (size_t i = 0; i < blinkPagesPerRegion; ++i)
-        m_inUse[i] = false;
 }
 
 PageMemoryRegion::~PageMemoryRegion()