Unified the structure of VirtualMemory implementations across platforms a bit.

src/platform-cygwin.cc

Index: src/platform-cygwin.cc
diff --git a/src/platform-cygwin.cc b/src/platform-cygwin.cc
index 042b2e54dea4b7ac706991516dc85e94ad5bd2ae..418a05e226148bb4b28fedb627d8eb62d195b7f8 100644
--- a/src/platform-cygwin.cc
+++ b/src/platform-cygwin.cc
@@ -319,15 +319,11 @@ int OS::StackWalk(Vector<OS::StackFrame> frames) {
 // This causes VirtualMemory::Commit to not always commit the memory region
 // specified.
 
-bool VirtualMemory::IsReserved() {
-  return address_ != NULL;
-}
+VirtualMemory::VirtualMemory() : address_(NULL), size_(0) { }
 
 
-VirtualMemory::VirtualMemory(size_t size) {
-  address_ = VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_NOACCESS);
-  size_ = size;
-}
+VirtualMemory::VirtualMemory(size_t size)
+    : address_(ReserveRegion(size)), size_(size) { }
 
 
 VirtualMemory::~VirtualMemory() {
@@ -337,6 +333,17 @@ VirtualMemory::~VirtualMemory() {
 }
 
 
+bool VirtualMemory::IsReserved() {
+  return address_ != NULL;
+}
+
+
+void VirtualMemory::Reset() {
+  address_ = NULL;
+  size_ = 0;
+}
+
+
 bool VirtualMemory::Commit(void* address, size_t size, bool is_executable) {
   int prot = is_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
   if (NULL == VirtualAlloc(address, size, MEM_COMMIT, prot)) {
@@ -365,6 +372,29 @@ bool VirtualMemory::Guard(void* address) {
 }
 
 
+void* VirtualMemory::ReserveRegion(size_t size) {
+  return VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_NOACCESS);
+}
+
+
+bool VirtualMemory::CommitRegion(void* base, size_t size, bool is_executable) {
+  UNIMPLEMENTED();
+  return false;
+}
+
+
+bool VirtualMemory::UncommitRegion(void* base, size_t size) {
+  UNIMPLEMENTED();
+  return false;
+}
+
+
+bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
+  UNIMPLEMENTED();
+  return false;
+}
+
+
 bool VirtualMemory::HasLazyCommits() {
   // TODO(alph): implement for the platform.
   return false;