Create stub for NativeUnwinderAndroid

This class will contain the Android-specific unwinding implementation,
which will rely on libunwindstack. libunwindstack will be pulled in as a
dynamic feature module (DFM).

Having a stub version of this class will allow us to create
StackSamplerAndroid. (StackSamplerAndroid will need to create a
StackSamplerImpl, which accepts an Unwinder as a constructor parameter.)

TBR=gab@chromium.org
R=wittman@chromium.org

Bug: 988574
Change-Id: Id929731e94232f457add7914eb426ebcdb0bf0f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726829Reviewed-by: Charlie Andrews <charliea@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682404}

base/BUILD.gn

@@ -613,6 +613,8 @@ jumbo_component("base") {
     "profiler/metadata_recorder.cc",
     "profiler/metadata_recorder.h",
     "profiler/native_unwinder.h",
+    "profiler/native_unwinder_android.cc",
+    "profiler/native_unwinder_android.h",
     "profiler/native_unwinder_mac.cc",
     "profiler/native_unwinder_mac.h",
     "profiler/native_unwinder_win.cc",

base/profiler/native_unwinder_android.cc

+// Copyright 2019 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.
+
+#include "base/profiler/native_unwinder_android.h"
+
+#include "base/profiler/native_unwinder.h"
+#include "base/profiler/profile_builder.h"
+#include "base/sampling_heap_profiler/module_cache.h"
+
+namespace base {
+
+bool NativeUnwinderAndroid::CanUnwindFrom(const Frame* current_frame) const {
+  return false;
+}
+
+UnwindResult NativeUnwinderAndroid::TryUnwind(RegisterContext* thread_context,
+                                              uintptr_t stack_top,
+                                              ModuleCache* module_cache,
+                                              std::vector<Frame>* stack) const {
+  return UnwindResult::ABORTED;
+}
+
+std::unique_ptr<Unwinder> CreateNativeUnwinder(ModuleCache* module_cache) {
+  return std::make_unique<NativeUnwinderAndroid>();
+}
+
+}  // namespace base

base/profiler/native_unwinder_android.h

+// Copyright 2019 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_PROFILER_NATIVE_UNWINDER_ANDROID_H_
+#define BASE_PROFILER_NATIVE_UNWINDER_ANDROID_H_
+
+#include "base/profiler/unwinder.h"
+
+namespace base {
+
+// Native unwinder implementation for Android, using libunwindstack.
+//
+// TODO(charliea): Implement this class.
+// See: https://crbug.com/989102
+class NativeUnwinderAndroid : public Unwinder {
+ public:
+  NativeUnwinderAndroid() = default;
+
+  NativeUnwinderAndroid(const NativeUnwinderAndroid&) = delete;
+  NativeUnwinderAndroid& operator=(const NativeUnwinderAndroid&) = delete;
+
+  // Unwinder
+  bool CanUnwindFrom(const Frame* current_frame) const override;
+  UnwindResult TryUnwind(RegisterContext* thread_context,
+                         uintptr_t stack_top,
+                         ModuleCache* module_cache,
+                         std::vector<Frame>* stack) const override;
+};
+
+}  // namespace base
+
+#endif  // BASE_PROFILER_NATIVE_UNWINDER_ANDROID_H_

base/profiler/thread_delegate_android.h

@@ -14,6 +14,7 @@ namespace base {
 // Android.
 //
 // TODO(charliea): Implement this class.
+// See: https://crbug.com/988574
 class BASE_EXPORT ThreadDelegateAndroid : public ThreadDelegate {
  public:
   class ScopedSuspendThread : public ThreadDelegate::ScopedSuspendThread {