Add WTF::DiscardableMemory.

Source/platform/exported/Platform.cpp

Index: Source/platform/exported/Platform.cpp
diff --git a/Source/platform/exported/Platform.cpp b/Source/platform/exported/Platform.cpp
index 7973183f8a251770df58646058a044e8f9364f86..3a42186b6b0717fdd7ab9ae252b7d45570dda3e7 100644
--- a/Source/platform/exported/Platform.cpp
+++ b/Source/platform/exported/Platform.cpp
@@ -30,14 +30,67 @@
 
 #include "config.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebDiscardableMemory.h"
+#include "wtf/Assertions.h"
+#include "wtf/Compiler.h"
+#include "wtf/DiscardableMemory.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/WTFPlatform.h"
+
+using namespace WTF;
 
 namespace blink {
 
-static Platform* s_platform = 0;
+namespace {
+
+Platform* s_platform = 0;
+
+class WTFDiscardableMemoryImpl : public DiscardableMemory {
+public:
+    explicit WTFDiscardableMemoryImpl(PassOwnPtr<WebDiscardableMemory> discardableMemory)
+        : m_discardableMemory(discardableMemory)
+    { }
+
+    virtual bool lock() OVERRIDE
+    {
+        return m_discardableMemory->lock();
+    }
+
+    virtual void* data() OVERRIDE
+    {
+        return m_discardableMemory->data();
+    }
+
+    virtual void unlock() OVERRIDE
+    {
+        return m_discardableMemory->unlock();
+    }
+
+private:
+    OwnPtr<WebDiscardableMemory> m_discardableMemory;
+};
+
+// WTFPlatformImpl is nothing more than a wrapper around blink::Platform.
+class WTFPlatformImpl : public WTFPlatform {
+public:
+    virtual PassOwnPtr<DiscardableMemory> allocateAndLockDiscardableMemory(size_t bytes) OVERRIDE
+    {
+        ASSERT(s_platform);
+        OwnPtr<WebDiscardableMemory> memory(adoptPtr(s_platform->allocateAndLockDiscardableMemory(bytes)));
+        if (!memory)
+            return PassOwnPtr<DiscardableMemory>();
+
+        return adoptPtr(new WTFDiscardableMemoryImpl(memory.release()));
+    }
+};
+
+} // namespace
 
 void Platform::initialize(Platform* platform)
 {
     s_platform = platform;
+    WTFPlatform::setInstance(new WTFPlatformImpl());
 }
 
 void Platform::shutdown()