Add support for file locking

runtime/bin/file_win.cc

Index: runtime/bin/file_win.cc
diff --git a/runtime/bin/file_win.cc b/runtime/bin/file_win.cc
index 7a4b0f033f1975cb2afe798e16f222a6da249f5d..62e7961f84e92a7161ec996e91ad08e34e619867 100644
--- a/runtime/bin/file_win.cc
+++ b/runtime/bin/file_win.cc
@@ -17,6 +17,7 @@
 #include "bin/builtin.h"
 #include "bin/log.h"
 #include "bin/utils.h"
+#include "platform/utils.h"
 
 
 namespace dart {
@@ -105,6 +106,44 @@ bool File::Flush() {
 }
 
 
+bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
+  ASSERT(handle_->fd() >= 0);
+  ASSERT(end == -1 || end > start);
+  HANDLE handle = reinterpret_cast<HANDLE>(_get_osfhandle(handle_->fd()));
+  OVERLAPPED overlapped;
+  ZeroMemory(&overlapped, sizeof(OVERLAPPED));
+
+  overlapped.Offset = Utils::Low32Bits(start);
+  overlapped.OffsetHigh = Utils::High32Bits(start);
+
+  int64_t length = end == -1 ? 0 : end - start;
+  if (length == 0) length = kMaxInt64;
+  int32_t length_low = Utils::Low32Bits(length);
+  int32_t length_high = Utils::High32Bits(length);
+
+
+  BOOL rc;
+  switch (lock) {
+    case File::kLockUnlock:
+      rc = UnlockFileEx(handle, 0, length_low, length_high, &overlapped);
+      break;
+    case File::kLockShared:
+    case File::kLockExclusive: {
+      DWORD flags = LOCKFILE_FAIL_IMMEDIATELY;
+      if (lock == File::kLockExclusive) {
+        flags |= LOCKFILE_EXCLUSIVE_LOCK;
+      }
+      rc = LockFileEx(handle, flags, 0,
+                      length_low, length_high, &overlapped);
+      break;
+    }
+    default:
+      UNREACHABLE();
+  }
+  return rc;
+}
+
+
 int64_t File::Length() {
   ASSERT(handle_->fd() >= 0);
   struct __stat64 st;
@@ -437,7 +476,7 @@ char* File::LinkTarget(const char* pathname) {
   // Remove "\??\" from beginning of target.
   if (target_length > 4 && wcsncmp(L"\\??\\", target, 4) == 0) {
     target += 4;
-    target_length -=4;
+    target_length -= 4;
   }
   int utf8_length = WideCharToMultiByte(CP_UTF8,
                                         0,