ServiceConnection: add process-specific memory fields

Add three new fields to the process fetcher: total memory, resident
memory and free memory. All fields are reported in KiB.

Bug: chromium:1102518
Change-Id: I894fdb4ed5605f12d95bdac4de67952e0414eff8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417319Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Paul Moy <pmoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808546}

chromeos/services/cros_healthd/public/mojom/cros_healthd_probe.mojom

@@ -115,6 +115,13 @@ struct ProcessInfo {
   uint64 uptime_ticks;
   // State of the process.
   ProcessState state;
+  // Total memory allocated to the process, in KiB.
+  uint32 total_memory_kib;
+  // Amount of resident memory currently used by the process, in KiB.
+  uint32 resident_memory_kib;
+  // Unused memory available to the process, in KiB. This will always be
+  // |total_memory_kib| - |resident_memory_kib|.
+  uint32 free_memory_kib;
 };
 
 // Battery probe result. Can either be populated with the BatteryInfo or an