Add trim support to MemoryBuffer There are usecases where we need a MemoryBuffer to be trimmed to a smaller size. In such cases there is no need to perform a resize, which would trigger a reallocation. Instead just update MemoryBuffer's size. Bug: angleproject:4722 Change-Id: I5b6cca121977903ffa7663591eaec62f6ffda97a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5513269 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: mohan maiya <m.maiya@samsung.com>