Do not unnecessarily convert from size_t to int64_t

ExternalMemoryAccounter::Increase() and ExternalMemoryAccounter::Decrease() expect a size_t argument instead of int64_t, so pass them directly instead of doing an unnecessary static_cast.

The cast to int64_t was required earlier before the introduction of the ExternalMemoryAccounter abstraction. Conversion to int64_t is not required in the newer API as it is done inside the Increase method

Change-Id: Icbcabad2454b98854e896455293b84a471a83ec1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6880517
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Commit-Queue: Raphael Kubo da Costa <kubo@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1510383}