[tracing] Add native allocation tracing mode.

base/trace_event/heap_profiler_allocation_context.cc

Index: base/trace_event/heap_profiler_allocation_context.cc
diff --git a/base/trace_event/heap_profiler_allocation_context.cc b/base/trace_event/heap_profiler_allocation_context.cc
index 038c083f0fa83241f9fef46c0ed239572d282d62..b6b711284d2568a88fb460e7855456a335e836ee 100644
--- a/base/trace_event/heap_profiler_allocation_context.cc
+++ b/base/trace_event/heap_profiler_allocation_context.cc
@@ -12,6 +12,18 @@
 namespace base {
 namespace trace_event {
 
+bool operator < (const StackFrame& lhs, const StackFrame& rhs) {
+  return lhs.value < rhs.value;
+}
+
+bool operator == (const StackFrame& lhs, const StackFrame& rhs) {
+  return lhs.value == rhs.value;
+}
+
+bool operator != (const StackFrame& lhs, const StackFrame& rhs) {
+  return lhs.value != rhs.value;
+}
+
 // Constructor that does not initialize members.
 AllocationContext::AllocationContext() {}
 
@@ -20,7 +32,7 @@ AllocationContext AllocationContext::Empty() {
   AllocationContext ctx;
 
   for (size_t i = 0; i < arraysize(ctx.backtrace.frames); i++)
-    ctx.backtrace.frames[i] = nullptr;
+    ctx.backtrace.frames[i] = StackFrame::Empty();
 
   ctx.type_name = nullptr;
 
@@ -43,6 +55,11 @@ bool operator==(const AllocationContext& lhs, const AllocationContext& rhs) {
 namespace BASE_HASH_NAMESPACE {
 using base::trace_event::AllocationContext;
 using base::trace_event::Backtrace;
+using base::trace_event::StackFrame;
+
+size_t hash<StackFrame>::operator()(const StackFrame& frame) const {
+  return this->hash<const void*>::operator()(frame.value);
+}
 
 size_t hash<Backtrace>::operator()(const Backtrace& backtrace) const {
   return base::SuperFastHash(reinterpret_cast<const char*>(backtrace.frames),