Blink gardening: updated expectations

BUG=391223
TBR=morrita
NOTRY=true

Review URL: https://codereview.chromium.org/685853003

git-svn-id: svn://svn.chromium.org/blink/trunk@184719 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: fix logic of determining content root for trace layers

We can't rely on draws_content property of layers we get from
tracing, as it may be true for non-content layers. Let's also
check the owner node. However, since there may be cases where
we lack the owner node info, be prepared to draw the entire
layer tree in case we failed to locate content root.

BUG=

Review URL: https://codereview.chromium.org/687963002

git-svn-id: svn://svn.chromium.org/blink/trunk@184720 bbb929c8-8fbe-4397-9dbb-9b2b20218538