Use a common buffer across all instances for stack-copy.

base/profiler/native_stack_sampler_posix.cc

Index: base/profiler/native_stack_sampler_posix.cc
diff --git a/base/profiler/native_stack_sampler_posix.cc b/base/profiler/native_stack_sampler_posix.cc
index 54abb2e3d3ad72bb46b0181b65bb81c6f0b718a5..504b9b97abec5858e7f04da0ecfe809f7ffa7c8f 100644
--- a/base/profiler/native_stack_sampler_posix.cc
+++ b/base/profiler/native_stack_sampler_posix.cc
@@ -13,4 +13,9 @@ std::unique_ptr<NativeStackSampler> NativeStackSampler::Create(
   return std::unique_ptr<NativeStackSampler>();
 }
 
+std::unique_ptr<NativeStackSampler::StackBuffer>
+NativeStackSampler::CreateStackBuffer() {
+  return nullptr;
+}
+
 }  // namespace base