[tracing] Add native allocation tracing mode.

base/base_switches.cc

Index: base/base_switches.cc
diff --git a/base/base_switches.cc b/base/base_switches.cc
index d1a38e4b21e4c2b44a4897f98cf4f59d2bc2567d..fa0bc3337189bc9986b8a655d93342ecfa127edb 100644
--- a/base/base_switches.cc
+++ b/base/base_switches.cc
@@ -20,6 +20,10 @@ const char kEnableCrashReporter[]           = "enable-crash-reporter";
 // the memory-infra category is enabled.
 const char kEnableHeapProfiling[]           = "enable-heap-profiling";
 
+// Report native (walk the stack) allocation traces. By default pseudo stacks
+// derived from trace events are reported.
+const char kEnableHeapProfilingModeNative[] = "native";
+
 // Generates full memory crash dump.
 const char kFullMemoryCrashReport[]         = "full-memory-crash-report";