Support needed for VirtualAlloc/VirtualFree analysis

VirtualFree and VirtualAlloc stacks can be critical in understanding memory consumption. VirtualFree is particularly interesting for programmatic trace analysis because it cannot be analyzed using WPA - if you just have the free but not the alloc then the data is hidden.

I recently got desperate and wrote code to analyze "xperf -a dumper" output (script is at https://github.com/google/UIforETW/blob/main/bin/VirtualFreeStacks.py). The results were incredibly useful (see crbug.com/1179934) and may help understand a significant memory issue in Chrome and/or Windows, but writing text parsing code to analyze ETW traces seems like the wrong solution at this time.

Text parsing code tends to be more fragile and it also requires additional steps and usually has significantly worse performance than the trace processor library. Text parsing also requires significant investigation in order to understand the layout of the output and what xperf options to use.

Start with bin/VirtualFreeStacks.py and the trace processor library, then compare the script's xperf -a dumper input with the WPA limitation described in the issue. Done means VirtualAlloc and VirtualFree stacks can be analyzed through the trace processor without relying on fragile text parsing.