AuthPolicyCredentialsManager: Use ImportantFileWriter

Switching from my own invented bike to a library function for
credentials and config files.

BUG=815158
TEST=manual

Change-Id: I32db516219a7db17d8b0dd7a3ed0f15c8430389f
Reviewed-on: https://chromium-review.googlesource.com/974108Reviewed-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Roman Sorokin <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547734}

chrome/browser/chromeos/authpolicy/auth_policy_credentials_manager.cc

@@ -5,7 +5,7 @@
 #include "chrome/browser/chromeos/authpolicy/auth_policy_credentials_manager.h"
 
 #include "ash/public/cpp/vector_icons/vector_icons.h"
-#include "base/files/file_util.h"
+#include "base/files/important_file_writer.h"
 #include "base/location.h"
 #include "base/memory/singleton.h"
 #include "base/path_service.h"
@@ -81,33 +81,14 @@ void SigninNotificationDelegate::ButtonClick(int button_index) {
 }
 
 // Writes |blob| into file <UserPath>/kerberos/|file_name|. First writes into
-// temporary file and then replace existing one.
+// temporary file and then replaces existing one.
 void WriteFile(const std::string& file_name, const std::string& blob) {
   base::FilePath dir;
   PathService::Get(base::DIR_HOME, &dir);
   dir = dir.Append(kKrb5Directory);
-  base::File::Error error;
-  if (!base::CreateDirectoryAndGetError(dir, &error)) {
-    LOG(ERROR) << "Failed to create '" << dir.value()
-               << "' directory: " << base::File::ErrorToString(error);
-    return;
-  }
-
-  base::FilePath temp_file;
-  if (!base::CreateTemporaryFileInDir(dir, &temp_file))
-    return;
-
-  if (base::WriteFile(temp_file, blob.data(), blob.size()) !=
-      static_cast<int>(blob.size())) {
-    LOG(ERROR) << "Failed to write file: " << temp_file.value();
-    return;
-  }
-
   base::FilePath dest_file = dir.Append(file_name);
-  if (!base::ReplaceFile(temp_file, dest_file, &error)) {
-    LOG(ERROR) << "Failed to replace '" << dest_file.value() << "' with '"
-               << temp_file.value()
-               << "' :" << base::File::ErrorToString(error);
+  if (!base::ImportantFileWriter::WriteFileAtomically(dest_file, blob)) {
+    LOG(ERROR) << "Failed to write file " << dest_file.value();
   }
 }
 
@@ -250,12 +231,16 @@ void AuthPolicyCredentialsManager::OnGetUserKerberosFilesCallback(
     const authpolicy::KerberosFiles& kerberos_files) {
   if (kerberos_files.has_krb5cc()) {
     base::PostTaskWithTraits(
-        FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
+        FROM_HERE,
+        {base::MayBlock(), base::TaskPriority::BACKGROUND,
+         base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN},
         base::BindOnce(&WriteFile, kKrb5CCFile, kerberos_files.krb5cc()));
   }
   if (kerberos_files.has_krb5conf()) {
     base::PostTaskWithTraits(
-        FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
+        FROM_HERE,
+        {base::MayBlock(), base::TaskPriority::BACKGROUND,
+         base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN},
         base::BindOnce(&WriteFile, kKrb5ConfFile, kerberos_files.krb5conf()));
   }
 }