Add a full Blimp integration test.

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 30f787b1c4fc02d1436bd23b404c88f107739aca..b451ab1aee803c32e7a8040b3122811391b2b61c 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -14,6 +14,9 @@ class HistogramSynchronizer;
 class NativeBackendKWallet;
 class ScopedAllowWaitForLegacyWebViewApi;
 
+namespace blimp {
+class BlimpBrowserTest;
+}
 namespace cc {
 class CompletionEvent;
 class SingleThreadTaskGraphRunner;
@@ -184,6 +187,7 @@ class BASE_EXPORT ThreadRestrictions {
  private:
   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to jam or brettw first.
   // BEGIN ALLOWED USAGE.
+  friend class blimp::BlimpBrowserTest;
   friend class content::BrowserShutdownProfileDumper;
   friend class content::BrowserSurfaceViewManager;
   friend class content::BrowserTestBase;