Implement committed physical memory stats for Linux.

src/platform-openbsd.cc

Index: src/platform-openbsd.cc
diff --git a/src/platform-openbsd.cc b/src/platform-openbsd.cc
index f96d9e3031a503c6f81282cc7b8d6bc09232d5c7..b8b1ffa7692471cdf9552ff388b557ad9ce1059d 100644
--- a/src/platform-openbsd.cc
+++ b/src/platform-openbsd.cc
@@ -504,6 +504,12 @@ bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
 }
 
 
+bool VirtualMemory::HasLazyCommits() {
+  // TODO(alph): implement for the platform.
+  return false;
+}
+
+
 class Thread::PlatformData : public Malloced {
  public:
   PlatformData() : thread_(kNoThread) {}