Support creating temporary files for sync file operations.

base/file_util_proxy.cc

Index: base/file_util_proxy.cc
diff --git a/base/file_util_proxy.cc b/base/file_util_proxy.cc
index 1d5b9cc3cea8ca3b11d232c2a10f87b5c5dba582..4dd57b792caf3ff65e45b8d830bd1e3a9bd6e534 100644
--- a/base/file_util_proxy.cc
+++ b/base/file_util_proxy.cc
@@ -167,8 +167,10 @@ class RelayCreateTemporary : public MessageLoopRelay {
  public:
   RelayCreateTemporary(
       scoped_refptr<base::MessageLoopProxy> message_loop_proxy,
+      bool async,
       base::FileUtilProxy::CreateTemporaryCallback* callback)
       : message_loop_proxy_(message_loop_proxy),
+        async_(async),
         callback_(callback),
         file_handle_(base::kInvalidPlatformFileValue) {
     DCHECK(callback);
@@ -190,8 +192,10 @@ class RelayCreateTemporary : public MessageLoopRelay {
     int file_flags =
         base::PLATFORM_FILE_CREATE_ALWAYS |
         base::PLATFORM_FILE_WRITE |
-        base::PLATFORM_FILE_ASYNC |
         base::PLATFORM_FILE_TEMPORARY;
+    if (async_) {
+      file_flags |= base::PLATFORM_FILE_ASYNC;
+    }
     base::PlatformFileError error_code = base::PLATFORM_FILE_OK;
     file_handle_ = base::CreatePlatformFile(file_path_, file_flags,
                                             NULL, &error_code);
@@ -206,6 +210,7 @@ class RelayCreateTemporary : public MessageLoopRelay {
 
  private:
   scoped_refptr<base::MessageLoopProxy> message_loop_proxy_;
+  bool async_;
   base::FileUtilProxy::CreateTemporaryCallback* callback_;
   base::PlatformFile file_handle_;
   FilePath file_path_;
@@ -742,9 +747,10 @@ bool FileUtilProxy::CreateOrOpen(
 // static
 bool FileUtilProxy::CreateTemporary(
     scoped_refptr<MessageLoopProxy> message_loop_proxy,
+    bool async,
     CreateTemporaryCallback* callback) {
   return Start(FROM_HERE, message_loop_proxy,
-               new RelayCreateTemporary(message_loop_proxy, callback));
+               new RelayCreateTemporary(message_loop_proxy, async, callback));
 }
 
 // static