Tweak cover blending in wpt/svg/render/reftests/blending-00[12].svg

Set 'mix-blend-mode' to 'normal' on the stroked rects that make up the
"edge cover". Hopefully this avoids aliasing artifacts on the edge cover
itself.

In blending-002.svg, localize the use of (non-auto) isolation to the
content of the test.

BUG=866928

Change-Id: I269e01a4d814f7fd8e202ffdf71c1a1d5dc48347
Reviewed-on: https://chromium-review.googlesource.com/1175825
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#583277}
2 files changed