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..b1053c3f48d984d04d4210df73d2b944eda57372 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -14,6 +14,10 @@ class HistogramSynchronizer;
 class NativeBackendKWallet;
 class ScopedAllowWaitForLegacyWebViewApi;
 
+namespace base {
+class StackSamplingProfiler;
+}
+
 namespace cc {
 class CompletionEvent;
 class SingleThreadTaskGraphRunner;
@@ -174,6 +178,7 @@ 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;