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The HidConnection knows the appropriate read buffer size and the
platform-specific implementation may already have a buffer that it is
waiting to return to the next caller. Passing a buffer in is therefore
unnecessary, one can be provided in the callback.

By standardizing on a buffer format which always includes the report ID
as the first byte (even when it is zero) most of the buffer copying can
be removed except in the case of OS X's persistent read buffer and
getting feature reports on Windows.

BUG=

Review URL: https://codereview.chromium.org/499713002

Cr-Commit-Position: refs/heads/master@{#291954}