[gn] Fix broken Windows builds

https://gn-review.googlesource.com/c/gn/+/14320 was submitted through CQ
despite failing to build on Windows. This fixes the broken bits.

Change-Id: Ibfd04f1480c9798c6ce8f68630fe4179f1b0eee2
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/14340
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>

src/base/files/file_util_win.cc

diff --git a/src/base/files/file_util_win.cc b/src/base/files/file_util_win.cc
index 150ddf6..c808bde 100644
--- a/src/base/files/file_util_win.cc
+++ b/src/base/files/file_util_win.cc
@@ -300,23 +300,25 @@
   // Although it is nearly impossible to get a duplicate name with GUID, we
   // still use a loop here in case it happens.
   for (int i = 0; i < 100; ++i) {
-    temp_name = dir.Append(FormatTemporaryFileName(UTF8ToWide(GenerateGUID())));
+    temp_name = dir.Append(
+        FilePath(UTF8ToUTF16(GenerateGUID()) + FILE_PATH_LITERAL(".tmp")));
     file.Initialize(temp_name, kFlags);
     if (file.IsValid())
       break;
   }
 
   if (!file.IsValid()) {
-    DPLOG(WARNING) << "Failed to get temporary file name in " << dir.value();
+    DPLOG(WARNING) << "Failed to get temporary file name in "
+                   << UTF16ToUTF8(dir.value());
     return file;
   }
 
-  wchar_t long_temp_name[MAX_PATH + 1];
-  const DWORD long_name_len =
-      GetLongPathName(temp_name.value().c_str(), long_temp_name, MAX_PATH);
+  char16_t long_temp_name[MAX_PATH + 1];
+  const DWORD long_name_len = GetLongPathName(
+      ToWCharT(temp_name.value().c_str()), ToWCharT(long_temp_name), MAX_PATH);
   if (long_name_len != 0 && long_name_len <= MAX_PATH) {
     *temp_file =
-        FilePath(FilePath::StringPieceType(long_temp_name, long_name_len));
+        FilePath(FilePath::StringViewType(long_temp_name, long_name_len));
   } else {
     // GetLongPathName() failed, but we still have a temporary file.
     *temp_file = std::move(temp_name);

src/gn/command_clean.cc

diff --git a/src/gn/command_clean.cc b/src/gn/command_clean.cc
index 8261845..e6c52fc 100644
--- a/src/gn/command_clean.cc
+++ b/src/gn/command_clean.cc
@@ -51,7 +51,8 @@
       base::FileEnumerator::FILES | base::FileEnumerator::DIRECTORIES);
   for (base::FilePath current = traversal.Next(); !current.empty();
        current = traversal.Next()) {
-    std::string basename = base::ToLowerASCII(current.BaseName().value());
+    base::FilePath::StringType basename =
+        base::ToLowerASCII(current.BaseName().value());
     if (std::none_of(std::begin(remaining), std::end(remaining),
                      [&](auto rem) { return basename == rem; })) {
       base::DeleteFile(current, true);

src/gn/commands.cc

diff --git a/src/gn/commands.cc b/src/gn/commands.cc
index 3840761..030f2d5 100644
--- a/src/gn/commands.cc
+++ b/src/gn/commands.cc
@@ -12,6 +12,7 @@
 #include "base/files/file_util.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "gn/builder.h"
 #include "gn/config_values_extractors.h"
@@ -329,6 +330,14 @@
   return std::nullopt;
 }
 
+std::string ToUTF8(base::FilePath::StringType in) {
+#if defined(OS_WIN)
+  return base::UTF16ToUTF8(in);
+#else
+  return in;
+#endif
+}
+
 }  // namespace
 
 CommandInfo::CommandInfo()
@@ -495,7 +504,7 @@
   // for ninja to call GN and regenerate ninja files.
   base::FilePath build_ninja_path(settings->GetFullPath(
       SourceFile(settings->build_dir().value() + "build.ninja")));
-  std::ifstream build_ninja_file(build_ninja_path.value());
+  std::ifstream build_ninja_file(ToUTF8(build_ninja_path.value()));
   if (!build_ninja_file) {
     // Couldn't open the build.ninja file.
     Err(Location(), "Couldn't open build.ninja in this directory.",