Reland of [tracing] Add native allocation tracing mode.

base/trace_event/heap_profiler_allocation_context.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TRACE_EVENT_HEAP_PROFILER_ALLOCATION_CONTEXT_H_
 #define BASE_TRACE_EVENT_HEAP_PROFILER_ALLOCATION_CONTEXT_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 11 matching lines @@
 // The backtrace in the allocation context is a snapshot of the stack. For now,
 // this is the pseudo stack where frames are created by trace event macros. In
 // the future, we might add the option to use the native call stack. In that
 // case, |Backtrace| and |AllocationContextTracker::GetContextSnapshot| might
 // have different implementations that can be selected by a compile time flag.
 
 // The number of stack frames stored in the backtrace is a trade off between
 // memory used for tracing and accuracy. Measurements done on a prototype
 // revealed that:
 //
-// - In 60 percent of the cases, stack depth <= 7.
-// - In 87 percent of the cases, stack depth <= 9.
-// - In 95 percent of the cases, stack depth <= 11.
+// - In 60 percent of the cases, pseudo stack depth <= 7.
+// - In 87 percent of the cases, pseudo stack depth <= 9.
+// - In 95 percent of the cases, pseudo stack depth <= 11.
 //
 // See the design doc (https://goo.gl/4s7v7b) for more details.
 
 // Represents (pseudo) stack frame. Used in Backtrace class below.
 //
 // Conceptually stack frame is identified by its value, and type is used
 // mostly to properly format the value. Value is expected to be a valid
 // pointer from process' address space.
 struct BASE_EXPORT StackFrame {
   enum class Type {
     TRACE_EVENT_NAME,   // const char* string
     THREAD_NAME,        // const char* thread name
+    PROGRAM_COUNTER,    // as returned by stack tracing (e.g. by StackTrace)
   };
 
   static StackFrame FromTraceEventName(const char* name) {
     return {Type::TRACE_EVENT_NAME, name};
   }
   static StackFrame FromThreadName(const char* name) {
     return {Type::THREAD_NAME, name};
   }
+  static StackFrame FromProgramCounter(const void* pc) {
+    return {Type::PROGRAM_COUNTER, pc};
+  }
 
   Type type;
   const void* value;
 };
 
 bool BASE_EXPORT operator < (const StackFrame& lhs, const StackFrame& rhs);
 bool BASE_EXPORT operator == (const StackFrame& lhs, const StackFrame& rhs);
 bool BASE_EXPORT operator != (const StackFrame& lhs, const StackFrame& rhs);
 
 struct BASE_EXPORT Backtrace {
   Backtrace();
 
   // If the stack is higher than what can be stored here, the bottom frames
-  // (the ones closer to main()) are stored. Based on the data above, a depth
-  // of 12 captures the full stack in the vast majority of the cases.
-  enum { kMaxFrameCount = 12 };
+  // (the ones closer to main()) are stored. Depth of 12 is enough for most
+  // pseudo traces (see above), but not for native traces, where we need more.
+  enum { kMaxFrameCount = 24 };
   StackFrame frames[kMaxFrameCount];
   size_t frame_count;
 };
 
 bool BASE_EXPORT operator==(const Backtrace& lhs, const Backtrace& rhs);
 
 // The |AllocationContext| is context metadata that is kept for every allocation
 // when heap profiling is enabled. To simplify memory management for book-
 // keeping, this struct has a fixed size.
 struct BASE_EXPORT AllocationContext {
@@ skipping 33 matching lines @@
 };
 
 template <>
 struct BASE_EXPORT hash<base::trace_event::AllocationContext> {
   size_t operator()(const base::trace_event::AllocationContext& context) const;
 };
 
 }  // BASE_HASH_NAMESPACE
 
 #endif  // BASE_TRACE_EVENT_HEAP_PROFILER_ALLOCATION_CONTEXT_H_