Use constexpr TaskTraits constructor in net.

net/disk_cache/blockfile/file_ios.cc

Index: net/disk_cache/blockfile/file_ios.cc
diff --git a/net/disk_cache/blockfile/file_ios.cc b/net/disk_cache/blockfile/file_ios.cc
index 47ff7f8edf9b142dbb9c1ee7502201dc565e6ad4..a5af353a2db8ce26399dbc31c8800f867a6d5e69 100644
--- a/net/disk_cache/blockfile/file_ios.cc
+++ b/net/disk_cache/blockfile/file_ios.cc
@@ -122,10 +122,8 @@ void FileInFlightIO::PostRead(disk_cache::File *file, void* buf, size_t buf_len,
   file->AddRef();  // Balanced on OnOperationComplete()
 
   base::PostTaskWithTraits(
-      FROM_HERE, base::TaskTraits()
-                     .WithShutdownBehavior(
-                         base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN)
-                     .MayBlock(),
+      FROM_HERE,
+      {base::MayBlock(), base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
       base::Bind(&FileBackgroundIO::Read, operation.get()));
   OnOperationPosted(operation.get());
 }
@@ -138,10 +136,8 @@ void FileInFlightIO::PostWrite(disk_cache::File* file, const void* buf,
   file->AddRef();  // Balanced on OnOperationComplete()
 
   base::PostTaskWithTraits(
-      FROM_HERE, base::TaskTraits()
-                     .WithShutdownBehavior(
-                         base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN)
-                     .MayBlock(),
+      FROM_HERE,
+      {base::MayBlock(), base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
       base::Bind(&FileBackgroundIO::Write, operation.get()));
   OnOperationPosted(operation.get());
 }