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

chrome/browser/task_manager/sampling/shared_sampler.h

Index: chrome/browser/task_manager/sampling/shared_sampler.h
diff --git a/chrome/browser/task_manager/sampling/shared_sampler.h b/chrome/browser/task_manager/sampling/shared_sampler.h
index fd6a8c3fbf573ee0d2157f0f354f1445b9fd3b76..217d103342fdee082b4a73364a7175faee427293 100644
--- a/chrome/browser/task_manager/sampling/shared_sampler.h
+++ b/chrome/browser/task_manager/sampling/shared_sampler.h
@@ -62,6 +62,14 @@ class SharedSampler : public base::RefCountedThreadSafe<SharedSampler> {
   // 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();