Currently, neither IsSharedCrossOrigin nor IsOpaque is set for an empty
script. Hence an exception thrown from it (e.g., an exception thrown
from native promise implementation) is treated as an error with
blink::kNotSharableCrossOrigin. On the other hand, as the script is
empty, there is no meaningful URL attached, which means the
ExecutionContext's URL is used as the script's name in
blink::SourceLocation::FromMessage. In other words, it works virtually
as same as blink::kSharableCrossOrigin corresponding to
ScriptOriginOptions with IsSharedCrossOrigin set and IsOpaque unset.

With this CL, a ScriptOriginOptions with IsSharedCrossOrigin is set
and IsOpaque is not set is attached to the empty script, as a
preliminary step to deprecate kNotSharableCrossOrigin.

Bug: chromium:875153,chromium:876248
Change-Id: I39279a43994337329b8bd9d28b6ca29f0ac30d9c
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/1201689Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55673}