PM: Remove last PageSignalGenerator user.

LocalSiteCharacteristicsWebContentsObserver (L41r) is the last user of
the PageSignalGenerator (PSG). This CL replaces that functionality with
a dedicated graph observer in preparation for retiring the PSG.
The storage of load time performance estimates is also removed. The PSG
maintains state for this that will be rewritten as a graph decorator in
due course.

Bug: 931407
Change-Id: I9840b6e9833702efde4d1587a990108c655e3b44
Commit-Queue: Sigurður Ásgeirsson <>
Reviewed-by: Chris Hamilton <>
Cr-Commit-Position: refs/heads/master@{#653367}
6 files changed