components: Specify locking mode in calls to base::File::Lock().

The distinction between kShared and kExplicit is large enough that there
are significant readability advantages to having the default be explicit
in the code.

Bug: 1125315
Change-Id: I34c479032b90124c88eadac8897c6d579dbd1554
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2394197Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804728}

components/services/filesystem/file_impl.cc

@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "base/check_op.h"
+#include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/files/scoped_file.h"
 #include "build/build_config.h"
@@ -66,7 +67,7 @@ bool FileImpl::IsValid() const {
 
 #if !defined(OS_FUCHSIA)
 base::File::Error FileImpl::RawLockFile() {
-  return file_.Lock();
+  return file_.Lock(base::File::LockMode::kExclusive);
 }
 
 base::File::Error FileImpl::RawUnlockFile() {

components/services/storage/public/cpp/filesystem/filesystem_impl.cc

@@ -290,7 +290,7 @@ FileErrorOr<base::File> FilesystemImpl::LockFileLocal(
     return base::File::FILE_ERROR_IN_USE;
 
 #if !defined(OS_FUCHSIA)
-  base::File::Error error = file.Lock();
+  base::File::Error error = file.Lock(base::File::LockMode::kExclusive);
   if (error != base::File::FILE_OK)
     return error;
 #endif