Support parallel captures from the StackSamplingProfiler.

base/threading/thread_restrictions.h

Index: base/threading/thread_restrictions.h
diff --git a/base/threading/thread_restrictions.h b/base/threading/thread_restrictions.h
index 8f3beb1d1a24b686e5810dceb9b190d53e345e04..cfc6df9da1802e89d14a834458211e328fe4757b 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -92,6 +92,7 @@ class TaskTracker;
 
 class SequencedWorkerPool;
 class SimpleThread;
+class StackSamplingProfiler;
 class Thread;
 class ThreadTestHelper;
 
@@ -174,6 +175,7 @@ class BASE_EXPORT ThreadRestrictions {
  private:
   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to jam or brettw first.
   // BEGIN ALLOWED USAGE.
+  friend class base::StackSamplingProfiler;
   friend class content::BrowserShutdownProfileDumper;
   friend class content::BrowserSurfaceViewManager;
   friend class content::BrowserTestBase;