Update TSL FileExists to use absl::string_view.

Users passing `std::string` will not need updating, since `string_view` will perform an implicit conversion.

PiperOrigin-RevId: 864529553

Author: zacmustin

tsl/platform/BUILD

@@ -1215,6 +1215,8 @@ cc_library(
     name = "null_file_system",
     hdrs = ["null_file_system.h"],
     deps = [
+        "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@xla//xla/tsl/platform:env",
     ],
 )
@@ -1441,6 +1443,7 @@ cc_library(
     deps = [
         ":random",
         ":retrying_utils",
+        "@com_google_absl//absl/strings:string_view",
         "@xla//xla/tsl/platform:env",
         "@xla//xla/tsl/platform:errors",
         "@xla//xla/tsl/platform:status",
@@ -1456,7 +1459,6 @@ tsl_cc_test(
         ":str_util",
         "@com_google_googletest//:gtest_main",
         "@xla//xla/tsl/lib/core:status_test_util",
-        "@xla//xla/tsl/platform:env_impl",
         "@xla//xla/tsl/platform:test",
     ],
 )

tsl/platform/null_file_system.h

@@ -20,6 +20,8 @@ limitations under the License.
 #include <string>
 #include <vector>
 
+#include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "xla/tsl/platform/env.h"
 #include "xla/tsl/platform/file_system.h"
 #include "xla/tsl/platform/file_system_helper.h"
@@ -62,7 +64,7 @@ class NullFileSystem : public FileSystem {
         "NewReadOnlyMemoryRegionFromFile unimplemented");
   }
 
-  absl::Status FileExists(const string& fname,
+  absl::Status FileExists(absl::string_view fname,
                           TransactionToken* token) override {
     return errors::Unimplemented("FileExists unimplemented");
   }

tsl/platform/retrying_file_system.h

@@ -18,9 +18,9 @@ limitations under the License.
 
 #include <functional>
 #include <memory>
-#include <string>
 #include <vector>
 
+#include "absl/strings/string_view.h"
 #include "xla/tsl/platform/env.h"
 #include "xla/tsl/platform/errors.h"
 #include "xla/tsl/platform/file_system.h"
@@ -56,7 +56,7 @@ class RetryingFileSystem : public FileSystem {
       const string& filename, TransactionToken* token,
       std::unique_ptr<ReadOnlyMemoryRegion>* result) override;
 
-  absl::Status FileExists(const string& fname,
+  absl::Status FileExists(absl::string_view fname,
                           TransactionToken* token) override {
     return RetryingUtils::CallWithRetries(
         [this, &fname, token]() {

tsl/platform/retrying_file_system_test.cc

@@ -127,7 +127,7 @@ class MockFileSystem : public FileSystem {
     return calls_.ConsumeNextCall("NewReadOnlyMemoryRegionFromFile");
   }
 
-  absl::Status FileExists(const string& fname,
+  absl::Status FileExists(absl::string_view fname,
                           TransactionToken* token) override {
     return calls_.ConsumeNextCall("FileExists");
   }