[Discardable Shared Memory] Adding Windows support.

base/memory/discardable_shared_memory.h

Index: base/memory/discardable_shared_memory.h
diff --git a/base/memory/discardable_shared_memory.h b/base/memory/discardable_shared_memory.h
index 0b5ac9fba8e5f7d9f82245720b69bd9c4051b49b..8a1e2b0ccc19387f3e8cb403bcd033edb3f4337e 100644
--- a/base/memory/discardable_shared_memory.h
+++ b/base/memory/discardable_shared_memory.h
@@ -15,6 +15,10 @@
 #include <set>
 #endif
 
+#if defined(OS_WIN)
+#include "base/win/windows_version.h"
+#endif
+
 // Linux (including Android) support the MADV_REMOVE argument with madvise()
 // which has the behavior of reliably causing zero-fill-on-demand pages to
 // be returned after a call. Here we define
@@ -144,6 +148,12 @@ class BASE_EXPORT DiscardableSharedMemory {
   DFAKE_MUTEX(thread_collision_warner_);
   Time last_known_usage_;
 
+#if defined(OS_WIN)
+  // Static Windows version.
+  // Not const as we'll first initialize, then lazy init this value.
+  static base::win::Version osVersion;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(DiscardableSharedMemory);
 };