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According to the base/files/file.h, the GetLength() method should return
a negative number on failure.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.win:win10_chromium_x64_rel_ng

Review-Url: https://codereview.chromium.org/2404823002
Cr-Commit-Position: refs/heads/master@{#437512}