Fix C4434 warning about 32-bit shift assigned to 64-bits
Fix C4434 warning about 32-bit shift assigned to 64-bits

VS 2015 has a new or louder warning about 32-bit shifts that are then
assigned to a 64-bit target. This type of code triggers it:

int64_t size = 1 << shift_amount;

Because the '1' being shifted is a 32-bit int the result of the shift
will be a 32-bit result, so assigning it to a 64-bit variable is just
misleading.

In this case the code that triggers it is this:

  m_IAID.resize(1 << SBSYMCODELEN);

The destination is a size_t so the warning only shows up on 64-bit
builds and doesn't indicate a real bug. But, casting the '1' constant
to size_t makes the behavior/intent more obvious and consistent and
allows enabling C4334 in Chromium.

BUG=593448
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1843253002 .

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