[NativeFS] Return correct error when trying to create a file/directory.

Make sure this actually fails on posix, and return the correct error
code when trying to create a file or directory fails because the other
type already exists.

Bug: 1098001
Change-Id: I265c079a436e2107e1ee9c146e87c9e9ea3db7a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2317989
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791450}

storage/browser/file_system/native_file_util.cc

@@ -147,6 +147,10 @@ base::File::Error NativeFileUtil::EnsureFileExists(const base::FilePath& path,
     // If its parent does not exist, should return NOT_FOUND error.
     return base::File::FILE_ERROR_NOT_FOUND;
 
+  // If |path| is a directory, return an error.
+  if (base::DirectoryExists(path))
+    return base::File::FILE_ERROR_NOT_A_FILE;
+
   // Tries to create the |path| exclusively.  This should fail
   // with base::File::FILE_ERROR_EXISTS if the path already exists.
   base::File file(path, base::File::FLAG_CREATE | base::File::FLAG_READ);
@@ -180,7 +184,7 @@ base::File::Error NativeFileUtil::CreateDirectory(const base::FilePath& path,
 
   // If file exists at the path.
   if (path_exists && !base::DirectoryExists(path))
-    return base::File::FILE_ERROR_EXISTS;
+    return base::File::FILE_ERROR_NOT_A_DIRECTORY;
 
   if (!base::CreateDirectory(path))
     return base::File::FILE_ERROR_FAILED;

third_party/blink/web_tests/external/wpt/native-file-system/native_FileSystemDirectoryHandle-getDirectoryHandle-manual.https-expected.txt

-This is a testharness.js-based test.
-PASS User succesfully selected an empty directory.
-PASS User granted write access.
-PASS getDirectoryHandle(create=false) rejects for non-existing directories
-PASS getDirectoryHandle(create=true) creates an empty directory
-PASS getDirectoryHandle(create=false) returns existing directories
-PASS getDirectoryHandle(create=true) returns existing directories without erasing
-FAIL getDirectoryHandle() when a file already exists with the same name promise_rejects_dom: function "function() { throw e }" threw object "InvalidModificationError: An attempt was made to create a file or directory where an element already exists." that is not a DOMException TypeMismatchError: property "code" is equal to 13, expected 17
-PASS getDirectoryHandle() with empty name
-PASS getDirectoryHandle() with "." name
-PASS getDirectoryHandle() with ".." name
-PASS getDirectoryHandle(create=false) with a path separator when the directory exists
-PASS getDirectoryHandle(create=true) with a path separator
-Harness: the test ran to completion.
-

third_party/blink/web_tests/platform/linux/external/wpt/native-file-system/native_FileSystemDirectoryHandle-getFileHandle-manual.https-expected.txt

-This is a testharness.js-based test.
-PASS User succesfully selected an empty directory.
-PASS User granted write access.
-PASS getFileHandle(create=false) rejects for non-existing files
-PASS getFileHandle(create=true) creates an empty file for non-existing files
-PASS getFileHandle(create=false) returns existing files
-PASS getFileHandle(create=true) returns existing files without erasing
-PASS getFileHandle(create=false) when a directory already exists with the same name
-FAIL getFileHandle(create=true) when a directory already exists with the same name assert_unreached: Should have rejected: undefined Reached unreachable code
-PASS getFileHandle() with empty name
-PASS getFileHandle() with "." name
-PASS getFileHandle() with ".." name
-PASS getFileHandle(create=false) with a path separator when the file exists.
-PASS getFileHandle(create=true) with a path separator
-Harness: the test ran to completion.
-

third_party/blink/web_tests/platform/mac/external/wpt/native-file-system/native_FileSystemDirectoryHandle-getFileHandle-manual.https-expected.txt

-This is a testharness.js-based test.
-PASS User succesfully selected an empty directory.
-PASS User granted write access.
-PASS getFileHandle(create=false) rejects for non-existing files
-PASS getFileHandle(create=true) creates an empty file for non-existing files
-PASS getFileHandle(create=false) returns existing files
-PASS getFileHandle(create=true) returns existing files without erasing
-PASS getFileHandle(create=false) when a directory already exists with the same name
-FAIL getFileHandle(create=true) when a directory already exists with the same name assert_unreached: Should have rejected: undefined Reached unreachable code
-PASS getFileHandle() with empty name
-PASS getFileHandle() with "." name
-PASS getFileHandle() with ".." name
-PASS getFileHandle(create=false) with a path separator when the file exists.
-PASS getFileHandle(create=true) with a path separator
-Harness: the test ran to completion.
-

third_party/blink/web_tests/platform/win/external/wpt/native-file-system/native_FileSystemDirectoryHandle-getFileHandle-manual.https-expected.txt

-This is a testharness.js-based test.
-PASS User succesfully selected an empty directory.
-PASS User granted write access.
-PASS getFileHandle(create=false) rejects for non-existing files
-PASS getFileHandle(create=true) creates an empty file for non-existing files
-PASS getFileHandle(create=false) returns existing files
-PASS getFileHandle(create=true) returns existing files without erasing
-PASS getFileHandle(create=false) when a directory already exists with the same name
-FAIL getFileHandle(create=true) when a directory already exists with the same name promise_rejects_dom: function "function() { throw e }" threw object "NoModificationAllowedError: An attempt was made to write to a file or directory which could not be modified due to the state of the underlying filesystem." that is not a DOMException TypeMismatchError: property "code" is equal to 7, expected 17
-PASS getFileHandle() with empty name
-PASS getFileHandle() with "." name
-PASS getFileHandle() with ".." name
-PASS getFileHandle(create=false) with a path separator when the file exists.
-PASS getFileHandle(create=true) with a path separator
-Harness: the test ran to completion.
-