[tracing] Remove MemoryAllocatorDump::process_memory_dump

This function should not be exist as it is casusing misleading use of
this function. The MAD is passed around to objects to dump memory
instead of PMD being passed around like the case of Sync. The
ReportMemoryUsage method should not be changing the PMD object when it
is passed only MAD.

BUG=

Review-Url: https://codereview.chromium.org/2545173002
Cr-Commit-Position: refs/heads/master@{#437328}
8 files changed