Add a field platform_private_footprint_ to ProcessMemoryTotals.

base/trace_event/process_memory_totals.h

Index: base/trace_event/process_memory_totals.h
diff --git a/base/trace_event/process_memory_totals.h b/base/trace_event/process_memory_totals.h
index 329967a6ee74cbee73bfded84c20f3bfc6cb549f..207e39867d7cfce11775c38d86bef5d9ab23fc04 100644
--- a/base/trace_event/process_memory_totals.h
+++ b/base/trace_event/process_memory_totals.h
@@ -32,6 +32,30 @@ class BASE_EXPORT ProcessMemoryTotals {
   uint64_t resident_set_bytes() const { return resident_set_bytes_; }
   void set_resident_set_bytes(uint64_t value) { resident_set_bytes_ = value; }
 
+  // Platform-specific data that will be used to compute the
+  // PrivateMemoryFootprint.
+  struct PlatformPrivateFootprint {
+    // macOS 10.12+
+    uint64_t phys_footprint_bytes = 0;
+
+    // macOS [all versions]
+    uint64_t internal_bytes = 0;
+    uint64_t compressed_bytes = 0;
+
+    // Linux, Android, ChromeOS
+    // TODO(hjd): https://crbug.com/707019
+    uint64_t rss_anon_bytes = 0;
+    uint64_t vm_swap_bytes = 0;
+
+    // On Windows,
+    //   TBD: https://crbug.com/707022
+    // On iOS,
+    //   TBD: https://crbug.com/714961
+  };
+  PlatformPrivateFootprint& GetPlatformPrivateFootprint() {
+    return platform_private_footprint_;
+  }
+
   uint64_t peak_resident_set_bytes() const { return peak_resident_set_bytes_; }
   void set_peak_resident_set_bytes(uint64_t value) {
     peak_resident_set_bytes_ = value;
@@ -51,6 +75,10 @@ class BASE_EXPORT ProcessMemoryTotals {
   uint64_t peak_resident_set_bytes_;
   bool is_peak_rss_resetable_;
 
+  // Not emitted in the trace as this is intended to be an intermediary in
+  // computation of private memory footprint.
+  PlatformPrivateFootprint platform_private_footprint_;
+
   // Extra metrics for OS-specific statistics.
   std::map<const char*, uint64_t> extra_fields_;