[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..6bbeeb6b6c62f0dfe884df34dd8145e032b21232 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 traces

[Primiano Tucci (use gerrit), 2016/04/07 15:51:56]

s/pseudo traces/pseudo stacks derived from trace events/

[Dmitry Skiba, 2016/04/12 18:22:10]

Done.

+// are reported.
+const char kEnableHeapProfilingModeNative[] = "native";

[Primiano Tucci (use gerrit), 2016/04/07 15:51:56]

Not sure if this constant (which is the value part for kEnableHeapProfiling
should live here or where we use it. I'll leave this to base owners

+
 // Generates full memory crash dump.
 const char kFullMemoryCrashReport[]         = "full-memory-crash-report";