standardize on std::chrono_literals

Summary:
This is not at all clear from cppreference.com, but per
https://www.youtube.com/watch?v=dTeKf5Oek2c, it sounds to me like
recommended practice is to either:

`using namespace std::chrono_literals` (or string_literals or
whatever) to pull in a focused set of literals.

or

`using namespace std::literals` to pull in all standard literals.

or

`using namespace std` to pull in everything.

`using namespace std::literals::chrono_literals` is unnecessarily
verbose.

Adopt those standards in Eden.

Reviewed By: simpkins

Differential Revision: D8060944

fbshipit-source-id: 4d9dd4329698b7ff5e5c81b5b28780ca4d81a2a1

eden/fs/fuse/test/FuseChannelTest.cpp

@@ -21,7 +21,7 @@
 #include "eden/fs/testharness/TestDispatcher.h"
 
 using namespace facebook::eden;
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using folly::ByteRange;
 using folly::Future;
 using folly::Promise;

eden/fs/inodes/InodeMap.cpp

@@ -28,7 +28,7 @@ using folly::Promise;
 using folly::throwSystemErrorExplicit;
 using folly::Unit;
 using std::string;
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 
 namespace facebook {
 namespace eden {

eden/fs/inodes/test/EdenMountTest.cpp

@@ -25,7 +25,7 @@
 #include "eden/fs/testharness/TestMount.h"
 #include "eden/fs/testharness/TestUtil.h"
 
-using namespace std::literals;
+using namespace std::chrono_literals;
 using folly::Optional;
 
 namespace facebook {
@@ -260,7 +260,6 @@ TEST(EdenMount, testCreatingFileSetsTimestampsToNow) {
 
   testMount.initialize(makeTestHash("1"), lastCheckoutTime);
 
-  using namespace std::literals::chrono_literals;
   clock.advance(10min);
 
   auto newFile = testMount.getEdenMount()

eden/fs/inodes/test/FileInodeTest.cpp

@@ -26,7 +26,7 @@ using namespace facebook::eden;
 using folly::StringPiece;
 using folly::literals::string_piece_literals::operator""_sp;
 using std::chrono::duration_cast;
-using namespace std::literals;
+using namespace std::chrono_literals;
 
 std::ostream& operator<<(std::ostream& os, const timespec& ts) {
   os << folly::sformat("{}.{:09d}", ts.tv_sec, ts.tv_nsec);

eden/fs/inodes/test/FuseTest.cpp

@@ -19,7 +19,7 @@
 #include <folly/test/TestUtils.h>
 
 using namespace facebook::eden;
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using folly::Future;
 using folly::ScopedEventBaseThread;
 using folly::Unit;

eden/fs/inodes/test/InodeMapTest.cpp

@@ -23,7 +23,7 @@
 #include "eden/fs/testharness/TestUtil.h"
 #include "eden/fs/utils/Bug.h"
 
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using namespace facebook::eden;
 using folly::StringPiece;
 

eden/fs/inodes/test/RenameTest.cpp

@@ -21,7 +21,7 @@
 #include "eden/fs/testharness/TestUtil.h"
 #include "eden/fs/utils/Bug.h"
 
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using namespace facebook::eden;
 using folly::StringPiece;
 

eden/fs/store/test/DiffTest.cpp

@@ -20,7 +20,7 @@
 #include "eden/fs/testharness/TestUtil.h"
 
 using namespace facebook::eden;
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using folly::Future;
 using folly::StringPiece;
 using std::make_shared;

eden/fs/takeover/TakeoverServer.cpp

@@ -26,7 +26,7 @@
 #include "eden/fs/takeover/TakeoverHandler.h"
 #include "eden/fs/utils/FutureUnixSocket.h"
 
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 
 using apache::thrift::CompactSerializer;
 using folly::AsyncServerSocket;

eden/fs/takeover/test/TakeoverTest.cpp

@@ -29,7 +29,7 @@ using folly::test::TemporaryDirectory;
 using std::string;
 using ::testing::ElementsAre;
 using ::testing::ElementsAreArray;
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 
 namespace {
 /**

eden/fs/testharness/FakeFuse.cpp

@@ -17,7 +17,7 @@
 #include <sys/types.h>
 #include "eden/third-party/fuse_kernel_linux.h"
 
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using folly::ByteRange;
 using folly::StringPiece;
 using std::string;

eden/fs/testharness/TestMount.cpp

@@ -46,7 +46,7 @@ using folly::StringPiece;
 using folly::Unit;
 using folly::test::TemporaryDirectory;
 using folly::test::TemporaryFile;
-using namespace std::literals::chrono_literals;
+using namespace std::chrono_literals;
 using std::make_shared;
 using std::make_unique;
 using std::shared_ptr;