Make File.create() fail when a directory exists at the same path

runtime/bin/file_fuchsia.cc

Index: runtime/bin/file_fuchsia.cc
diff --git a/runtime/bin/file_fuchsia.cc b/runtime/bin/file_fuchsia.cc
index ff080439d07aa5cd0e0621da58dfe12955c0c93b..ceea0c3d6f37d10fee47b9b0e689dc27ed182079 100644
--- a/runtime/bin/file_fuchsia.cc
+++ b/runtime/bin/file_fuchsia.cc
@@ -208,9 +208,10 @@ File* File::OpenStdio(int fd) {
 
 
 bool File::Exists(const char* name) {
-  struct stat st;
-  if (NO_RETRY_EXPECTED(stat(name, &st)) == 0) {
-    return S_ISREG(st.st_mode);
+  struct stat64 st;
+  if (NO_RETRY_EXPECTED(stat64(name, &st)) == 0) {
+    // Everything but a directory and a link is a file to Dart.
+    return !S_ISDIR(st.st_mode) && !S_ISLNK(st.st_mode);
   } else {
     return false;
   }
@@ -218,11 +219,27 @@ bool File::Exists(const char* name) {
 
 
 bool File::Create(const char* name) {
-  int fd = NO_RETRY_EXPECTED(open(name, O_RDONLY | O_CREAT | O_CLOEXEC, 0666));
+  int fd =
+      NO_RETRY_EXPECTED(open64(name, O_RDONLY | O_CREAT | O_CLOEXEC, 0666));
   if (fd < 0) {
     return false;
   }
-  return (close(fd) == 0);
+  // File.create returns a File, so we shouldn't be giving the illusion that the
+  // call has created a file or that a file already exists if there is already
+  // an entity at the same path that is a directory or a link.
+  bool is_file = true;
+  struct stat64 st;
+  if (NO_RETRY_EXPECTED(fstat64(fd, &st)) == 0) {
+    if (S_ISDIR(st.st_mode)) {
+      errno = EISDIR;
+      is_file = false;
+    } else if (S_ISLNK(st.st_mode)) {
+      errno = ENOENT;
+      is_file = false;
+    }
+  }
+  FDUtils::SaveErrorAndClose(fd);
+  return is_file;
 }