Implement committed physical memory stats for Linux.

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index 49463be8e00fbf8ab022e71ba8af5fccaf0f2f09..f10b46e6f6bb2cd348e6fe852487d26798d9c2d8 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -1551,6 +1551,13 @@ bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
 }
 
 
+bool VirtualMemory::CommittedPhysicalSizeInRegion(
+    void* base, size_t size, size_t* physical) {
+  // TODO(alph): implement for the platform.
+  return false;
+}
+
+
 // ----------------------------------------------------------------------------
 // Win32 thread support.