Currently, because the source float_64_array has an iterator, it hits
the code in the "check_iterator" section of TypedArrayFrom which calls
IterableToList. This builds a temporary PACKED_ELEMENTS array (and boxes
all of the numeric values as HeapNumbers), then uses this as the source
array.

This patch checks if the source array is a TypedArray, and if the iterator
is the built-in one (where we know the iterator's behaviour). If both are
true then it bypasses the creation of this temporary array and uses the
original TypedArray as the source.

This allows it to take advantage of the existing fast code for copying one
typed array to another.

R=hablich@chromium.org, petermarshall@chromium.org

Bug: chromium:884671
Change-Id: I19a944c9d6d5d07699c7dc3ad7196fc871200b62
Reviewed-on: https://chromium-review.googlesource.com/c/1297312Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57022}