Rename ShadowDistributed to ShadowV0Distributed

There are other places which "shadow distributed" is used
(e.g. css/RuleSet.h), and those are renamed to "content pseudo" etc. in
https://codereview.chromium.org/1616743002/

For these tests in editing, renaming it to "ShadowV0" should
make more sense because it is tested against V0 distributed
node (i.e. <content>).

This is a name-only change and no functionality/test difference.

BUG=531990

Review URL: https://codereview.chromium.org/1610993003

Cr-Commit-Position: refs/heads/master@{#370656}
2 files changed