Merge ArrayBufferBuilder into FetchDataLoaderAsArrayBuffer

FetchDataLoaderAsArrayBuffer is the only user of ArrayBufferBuilder.
So rather than keeping this utility class in WTF,
we should just merge the ArrayBufferBuilder code into FetchDataLoaderAsArrayBuffer.

Bug: 937390
Change-Id: I2a89f2409280c5ac544be9294c3f17eaea366ff3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1536042
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yeol Park <peary2@gmail.com>
Auto-Submit: Yeol Park <peary2@gmail.com>
Cr-Commit-Position: refs/heads/master@{#644201}
5 files changed