UMA values for 50th percentile show ~7.5MB. That seems wrong, given that it should include DiscardableSharedMemory, which includes decoded images which are typically pretty big.

The number is computed here: https://cs.chromium.org/chromium/src/services/resource_coordinator/memory_instrumentation/queued_request_dispatcher.cc?type=cs&q=shared_footprint_kb+-file:src/out&g=0&l=480

* Is it reporting the effective_size rather than size? 
* Is it failing to include DiscardableSharedMemory and other sources of shared memory?
* Is the size computation wrong? https://cs.chromium.org/chromium/src/base/trace_event/process_memory_dump.cc?sq=package:chromium&g=0&l=114