Implement committed physical memory stats for Linux.

src/platform-cygwin.cc

Index: src/platform-cygwin.cc
diff --git a/src/platform-cygwin.cc b/src/platform-cygwin.cc
index 089ea38d9a1bb2e0eb11de6d6f1551b0a5268ee3..6c59ecf699427527c08a26f317e9a822448073fd 100644
--- a/src/platform-cygwin.cc
+++ b/src/platform-cygwin.cc
@@ -359,6 +359,13 @@ bool VirtualMemory::Guard(void* address) {
 }
 
 
+bool VirtualMemory::CommittedPhysicalSizeInRegion(
+    void* base, size_t size, size_t* physical) {
+  // TODO(alph): implement for the platform.
+  return false;
+}
+
+
 class Thread::PlatformData : public Malloced {
  public:
   PlatformData() : thread_(kNoThread) {}