tracing: Report ResourceClients and the reason for not deletable for web-caches

This CL adds
- Resource::reasonNotDeletable() (mostly corresponds to canDelete())
- ResourceClient::debugName() and its overrides
that are used in Resource::onMemoryDump().

This CL utilizes already-defined LayoutObject::debugName(), and makes it to be
an override of ResourceClient::debugName().

BUG=549445

Review URL: https://codereview.chromium.org/1413233005

Cr-Commit-Position: refs/heads/master@{#358735}
39 files changed