Revert of [Discardable Shared Memory] Adding Windows support.

base/memory/discardable_shared_memory.cc

Index: base/memory/discardable_shared_memory.cc
diff --git a/base/memory/discardable_shared_memory.cc b/base/memory/discardable_shared_memory.cc
index 24bd3e3c720e880839709e0e1fd49717661768a3..1b50da260e09b566807fb40e72a1ab0638db11d3 100644
--- a/base/memory/discardable_shared_memory.cc
+++ b/base/memory/discardable_shared_memory.cc
@@ -19,10 +19,6 @@
 
 #if defined(OS_ANDROID)
 #include "third_party/ashmem/ashmem.h"
-#endif
-
-#if defined(OS_WIN)
-#include "base/win/windows_version.h"
 #endif
 
 namespace base {
@@ -218,7 +214,6 @@
   DCHECK_EQ(locked_pages_.size(), locked_page_count_);
 #endif
 
-// Pin pages if supported.
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();
   if (SharedMemory::IsHandleValid(handle)) {
@@ -227,14 +222,6 @@
       return PURGED;
     }
   }
-#elif defined(OS_WIN)
-  if (base::win::GetVersion() >= base::win::VERSION_WIN8) {
-    if (!VirtualAlloc(reinterpret_cast<char*>(shared_memory_.memory()) +
-                          AlignToPageSize(sizeof(SharedState)) + offset,
-                      length, MEM_RESET_UNDO, PAGE_READWRITE)) {
-      return PURGED;
-    }
-  }
 #endif
 
   return SUCCESS;
@@ -253,25 +240,12 @@
 
   DCHECK(shared_memory_.memory());
 
-// Unpin pages if supported.
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();
   if (SharedMemory::IsHandleValid(handle)) {
     if (ashmem_unpin_region(
             handle.fd, AlignToPageSize(sizeof(SharedState)) + offset, length)) {
       DPLOG(ERROR) << "ashmem_unpin_region() failed";
-    }
-  }
-#elif defined(OS_WIN)
-  if (base::win::GetVersion() >= base::win::VERSION_WIN8) {
-    // Note: MEM_RESET is not technically gated on Win8.  However, this Unlock
-    // function needs to match the Lock behaviour (MEM_RESET_UNDO) to properly
-    // implement memory pinning.  It needs to bias towards preserving the
-    // contents of memory between an Unlock and next Lock.
-    if (!VirtualAlloc(reinterpret_cast<char*>(shared_memory_.memory()) +
-                          AlignToPageSize(sizeof(SharedState)) + offset,
-                      length, MEM_RESET, PAGE_READWRITE)) {
-      DPLOG(ERROR) << "VirtualAlloc() MEM_RESET failed in Unlock()";
     }
   }
 #endif
@@ -349,12 +323,6 @@
     return false;
   }
 
-// The next section will release as much resource as can be done
-// from the purging process, until the client process notices the
-// purge and releases its own references.
-// Note: this memory will not be accessed again.  The segment will be
-// freed asynchronously at a later time, so just do the best
-// immediately.
 #if defined(OS_POSIX) && !defined(OS_NACL)
 // Linux and Android provide MADV_REMOVE which is preferred as it has a
 // behavior that can be verified in tests. Other POSIX flavors (MacOSX, BSDs),
@@ -372,14 +340,6 @@
               AlignToPageSize(mapped_size_), MADV_PURGE_ARGUMENT)) {
     DPLOG(ERROR) << "madvise() failed";
   }
-#elif defined(OS_WIN)
-  // MEM_DECOMMIT the purged pages to release the physical storage,
-  // either in memory or in the paging file on disk.  Pages remain RESERVED.
-  if (!VirtualFree(reinterpret_cast<char*>(shared_memory_.memory()) +
-                       AlignToPageSize(sizeof(SharedState)),
-                   AlignToPageSize(mapped_size_), MEM_DECOMMIT)) {
-    DPLOG(ERROR) << "VirtualFree() MEM_DECOMMIT failed in Purge()";
-  }
 #endif
 
   last_known_usage_ = Time();