clang/win: Make dump_file_system.cc build.

clang/win: Make dump_file_system.cc build.

In clang/win/gn builds, this file warned:
../../storage/browser/fileapi/dump_file_system.cc(96,71) : error: invalid suffix on literal; C++11 requires a space between literal and identifier [-Werror,-Wreserved-user-defined-literal]
      ShowMessageAndExit(base::StringPrintf("GetFileInfo failed for %"PRId64,
                                                                      ^

In gyp builds, nothing in build/all.gyp depends on this target, and in non-Win
gn src/BUILD.gn blacklists this target.  So this warning is only seen on
clang/win gn builds.

No behavior change.

BUG=491209
TBR=tzik

Review URL: https://codereview.chromium.org/1303063010 .

Cr-Commit-Position: refs/heads/master@{#346781}