message: Add Fuchsia support to memory_usage.
  Implement GetProcessResidentSizeBytes for Fuchsia.
  Cr-Commit-Position: refs/heads/main@{#39154}
diff: #include <windows.h>
  #include <psapi.h> // must come after windows.h
  // clang-format on
  +#elif defined(WEBRTC_FUCHSIA)
  +#include <lib/zx/process.h>
  +#include <zircon/status.h>
  #endif
  #include "rtc_base/logging.h"
  @@ -61,8 +64,16 @@ int64_t GetProcessResidentSizeBytes() {
  }
  return pmc.WorkingSetSize;
  #elif defined(WEBRTC_FUCHSIA)
  - RTC_LOG_ERR(LS_ERROR) << "GetProcessResidentSizeBytes() not implemented";
  - return 0;
  + zx_info_task_stats_t task_stats;
  + zx_status_t status = zx::process::self()->get_info(
  + ZX_INFO_TASK_STATS, &task_stats, sizeof(task_stats), nullptr, nullptr);
  + if (status == ZX_OK) {
  + return task_stats.mem_mapped_bytes;
  + } else {
  + RTC_LOG_ERR(LS_ERROR) << "get_info() failed: "
  + << zx_status_get_string(status);
  + return -1;
  + }
  #else
  // Not implemented yet.
  static_assert(false,
  