Remove unused member variable in class StackSamplingProfiler

Change-Id: If62a55a7c407096cc89af6df245acc4d9dec32d3
Reviewed-on: https://chromium-review.googlesource.com/1091932Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Xi Cheng <chengx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565681}

base/profiler/stack_sampling_profiler.h

@@ -23,7 +23,6 @@
 
 namespace base {
 
-class NativeStackSampler;
 class NativeStackSamplerTestDelegate;
 
 // StackSamplingProfiler periodically stops a thread to sample its stack, for
@@ -297,10 +296,6 @@ class BASE_EXPORT StackSamplingProfiler {
   // when that sampling is complete and the callback done.
   WaitableEvent profiling_inactive_;
 
-  // Object that does the native sampling. This is created during construction
-  // and later passed to the sampling thread when profiling is started.
-  std::unique_ptr<NativeStackSampler> native_sampler_;
-
   // An ID uniquely identifying this profiler to the sampling thread. This
   // will be an internal "null" value when no collection has been started.
   int profiler_id_;