Fix PropertyTree::ToString() and LayerTreeHostImpl::FrameData::ToString()

We should use TracedValue(0, /*force_json=*/true) to ensure it can be
converted to JSON, which is enforced after crrev.com/c/1888271.

Change-Id: I297b090200e107d4398f9a8e4accd34b4c427530
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1955487
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722781}
3 files changed