NaCl cleanup: Remove a reference to the NaClHandle type
NaCl cleanup: Remove a reference to the NaClHandle type

Use base::PlatformFile instead.  It's equivalent, but preferred
because we're calling IPC::PlatformFileForTransitToPlatformFile()
here.

This removes a reference to a NaCl-side typedef.

BUG=302078
TEST=build

Review URL: https://codereview.chromium.org/1617183002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#370868}

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