Add support for file locking

runtime/bin/file.h

Index: runtime/bin/file.h
diff --git a/runtime/bin/file.h b/runtime/bin/file.h
index 990b7b220d43a63c3bf84bd8d5a3427a816602dc..7a8107fd91f4f16629aec759ee9ba50e46aa1281 100644
--- a/runtime/bin/file.h
+++ b/runtime/bin/file.h
@@ -69,6 +69,15 @@ class File {
     kStatSize = 6
   };
 
+  enum LockType {
+    // These match the constants in FileStat in file_impl.dart.
+    kLockMin = 0,
+    kLockUnlock = 0,
+    kLockShared = 1,
+    kLockExclusive = 2,
+    kLockMax = 2
+  };
+
   ~File();
 
   intptr_t GetFD();
@@ -105,6 +114,9 @@ class File {
   // Flush contents of file.
   bool Flush();
 
+  // Lock range of a file.
+  bool Lock(LockType lock, int64_t start, int64_t end);
+
   // Returns whether the file has been closed.
   bool IsClosed();
 
@@ -168,6 +180,7 @@ class File {
   static CObject* TypeRequest(const CObjectArray& request);
   static CObject* IdenticalRequest(const CObjectArray& request);
   static CObject* StatRequest(const CObjectArray& request);
+  static CObject* LockRequest(const CObjectArray& request);
 
  private:
   explicit File(FileHandle* handle) : handle_(handle) { }