Add unit-test for SharedSampler handling of zero-thread processes.

chrome/browser/task_manager/sampling/shared_sampler.h

 // Copyright 2016 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 CHROME_BROWSER_TASK_MANAGER_SAMPLING_SHARED_SAMPLER_H_
 #define CHROME_BROWSER_TASK_MANAGER_SAMPLING_SHARED_SAMPLER_H_
 
 #include <map>
 #include <memory>
 #include <utility>
@@ skipping 44 matching lines @@
                          const OnStartTimeCallback& on_start_time,
                          const OnCpuTimeCallback& on_cpu_time);
 
   // Unregisters task group specific callbacks.
   void UnregisterCallbacks(base::ProcessId process_id);
 
   // Refreshes the expensive process' stats (for now only idle wakeups per
   // second) on the worker thread.
   void Refresh(base::ProcessId process_id, int64_t refresh_flags);
 
+#if defined(OS_WIN)
+  // Specifies a function to use in place of NtQuerySystemInformation.
+  typedef int (*QuerySystemInformationForTest)(unsigned char* buffer,
+                                               int buffer_size);
+  static void SetQuerySystemInformationForTest(
+      QuerySystemInformationForTest query_system_information);
+#endif  // defined(OS_WIN)
+
  private:
   friend class base::RefCountedThreadSafe<SharedSampler>;
   ~SharedSampler();
 
 #if defined(OS_WIN)
   // The UI-thread callbacks in TaskGroup registered with RegisterCallbacks and
   // to be called when refresh on the worker thread is done.
   struct Callbacks {
     Callbacks();
     Callbacks(Callbacks&& other);
@@ skipping 73 matching lines @@
   // To assert we're running on the correct thread.
   base::SequenceChecker worker_pool_sequenced_checker_;
 #endif  // defined(OS_WIN)
 
   DISALLOW_COPY_AND_ASSIGN(SharedSampler);
 };
 
 }  // namespace task_manager
 
 #endif  // CHROME_BROWSER_TASK_MANAGER_SAMPLING_SHARED_SAMPLER_H_