Cleaner fall-back stack capture for --enable-heap-profiling=native.

base/trace_event/heap_profiler_allocation_context_tracker.cc

Index: base/trace_event/heap_profiler_allocation_context_tracker.cc
diff --git a/base/trace_event/heap_profiler_allocation_context_tracker.cc b/base/trace_event/heap_profiler_allocation_context_tracker.cc
index b47dc16eddd02b2565bd18511d0490a17c488056..30d52a103952dc928d055e228add21b989ed5e6a 100644
--- a/base/trace_event/heap_profiler_allocation_context_tracker.cc
+++ b/base/trace_event/heap_profiler_allocation_context_tracker.cc
@@ -203,30 +203,34 @@ bool AllocationContextTracker::GetContextSnapshot(AllocationContext* ctx) {
         // from main() and up. Stack unwinding produces top frames, i.e.
         // from this point and up until main(). We request many frames to
         // make sure we reach main(), and then copy bottom portion of them.
-        const void* frames[128];
-        static_assert(arraysize(frames) >= Backtrace::kMaxFrameCount,
-                      "not requesting enough frames to fill Backtrace");
-#if HAVE_TRACE_STACK_FRAME_POINTERS && !defined(OS_NACL)
-        size_t frame_count = debug::TraceStackFramePointers(
-            frames,
-            arraysize(frames),
-            1 /* exclude this function from the trace */ );
-#else
-        size_t frame_count = 0;
-        NOTREACHED();
-#endif
-
-        // Copy frames backwards
-        size_t backtrace_capacity = backtrace_end - backtrace;
-        int32_t top_frame_index = (backtrace_capacity >= frame_count)
-                                      ? 0
-                                      : frame_count - backtrace_capacity;
-        for (int32_t i = frame_count - 1; i >= top_frame_index; --i) {
-          const void* frame = frames[i];
-          *backtrace++ = StackFrame::FromProgramCounter(frame);
-        }
-        break;
+#if !defined(OS_NACL)
+#if HAVE_TRACE_STACK_FRAME_POINTERS()
+      const void* frames[128];
+      static_assert(arraysize(frames) >= Backtrace::kMaxFrameCount,
+                    "not requesting enough frames to fill Backtrace");
+      size_t frame_count = debug::TraceStackFramePointers(
+          frames, arraysize(frames),
+          1 /* exclude this function from the trace */);
+#else   // HAVE_TRACE_STACK_FRAME_POINTERS()
+      // Fall-back to capturing the stack with base::debug::StackTrace,
+      // which is likely slower, but more reliable.
+      base::debug::StackTrace stack_trace(Backtrace::kMaxFrameCount);
+      size_t frame_count = 0u;
+      const void* const* frames = stack_trace.Addresses(&frame_count);
+#endif  // HAVE_TRACE_STACK_FRAME_POINTERS()
+
+      // Copy frames backwards
+      size_t backtrace_capacity = backtrace_end - backtrace;
+      int32_t top_frame_index = (backtrace_capacity >= frame_count)
+                                    ? 0
+                                    : frame_count - backtrace_capacity;
+      for (int32_t i = frame_count - 1; i >= top_frame_index; --i) {
+        const void* frame = frames[i];
+        *backtrace++ = StackFrame::FromProgramCounter(frame);
       }
+#endif  // !defined(OS_NACL)
+      break;
+    }
   }
 
   ctx->backtrace.frame_count = backtrace - std::begin(ctx->backtrace.frames);