Rename ReadableStreamDefaultReader to ReadableStreamReader

Rename the implementation of ReadableStreamDefaultReader to
ReadableStreamReader. Move the ReadableStreamReaderGeneric operations
into the class. This will help prepare for the future addition of
ReadableStreamBYOBReader.

This CL only moves and renames code. No functional changes.

BUG=902633

Change-Id: Icc42ee61886be21618ca417e1783f2a1056bc1ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573558
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652489}
10 files changed