Add function to compute proportional set size for OS_WIN

components/tracing/common/process_metrics_memory_dump_provider.cc

Index: components/tracing/common/process_metrics_memory_dump_provider.cc
diff --git a/components/tracing/common/process_metrics_memory_dump_provider.cc b/components/tracing/common/process_metrics_memory_dump_provider.cc
index d2c00c347f0db3f7f9b13286e2af3edc4ac089b3..2d26cbf9a5d87a8d59f5dac7d9082e81314a10b2 100644
--- a/components/tracing/common/process_metrics_memory_dump_provider.cc
+++ b/components/tracing/common/process_metrics_memory_dump_provider.cc
@@ -298,6 +298,18 @@ bool ProcessMetricsMemoryDumpProvider::DumpProcessTotals(
                                               nullptr /* shared_bytes */);
   if (res)
     pmd->process_totals()->SetExtraFieldInBytes("private_bytes", private_bytes);
+#elif defined(OS_WIN)
+  if (args.level_of_detail ==
+      base::trace_event::MemoryDumpLevelOfDetail::DETAILED) {
+    uint64_t pss_bytes = 0;
+    bool res = process_metrics_->GetProportionalSetSizeBytes(&pss_bytes);
+    if (res) {
+      base::trace_event::ProcessMemoryMaps::VMRegion region;

[Primiano Tucci (use gerrit), 2016/12/06 17:47:57]

If I read the code correctly now within this function we are grabbing and
iterating over WorkingSetInformationBuffer twice:
once up in line 268 upon GetWorkingSetSize() and once here.
Is there a way we could expose/wrap the WorkingSetInformationBuffer, or the
result of postprocessing it?

[chengx, 2016/12/06 19:40:09]

My understanding is that line 268 calls GetWorkingSetSize() defined in
process_metrics_win.cc. GetWorkingSetSize() itself calls a WinAPI
GetProcessMemoryInfo. It seems WorkingSetInformationBuffer is not involved here.
Please correct me if I am wrong.

[Primiano Tucci (use gerrit), 2016/12/08 16:36:01]

Ahh you are right. I confused GetWorkingSetSize() with GetWorkingSetKBytes()
when reading the code. the latter does use the WSIBuffer. So you are right it's
all good.

+      region.byte_stats_proportional_resident = pss_bytes;
+      pmd->process_mmaps()->AddVMRegion(region);
+    }
+  }
+
 #endif  // defined(OS_LINUX) || defined(OS_ANDROID)

[Primiano Tucci (use gerrit), 2016/12/06 17:47:57]

plz can you remove the comment from this #endif as it doesn't apply anymore
after the various #else branches? 

[chengx, 2016/12/06 19:40:09]

Done.

 #endif  // !defined(OS_IOS)