Merged all PointerToId functions into TraceHelper::PointerToString.

There are many places in scheduler/renderer that need to make a string
out of a pointer for tracing purposes. This creates a shared function
for them.

This was noticed while experimenting with jumbo builds which can not
handle reused symbol names in the global or global anonymous scope.

Review-Url: https://codereview.chromium.org/2837323002
Cr-Commit-Position: refs/heads/master@{#470948}
9 files changed