Clean up thread handling in Blimp browser tests.

blimp/engine/browser_tests/blimp_browser_test.h

Index: blimp/engine/browser_tests/blimp_browser_test.h
diff --git a/blimp/engine/browser_tests/blimp_browser_test.h b/blimp/engine/browser_tests/blimp_browser_test.h
index 820ec27e9fbd7fa285924664af12d0d1818812fd..a2990aa7210ee70867b00327d1d216bbd05c7ce0 100644
--- a/blimp/engine/browser_tests/blimp_browser_test.h
+++ b/blimp/engine/browser_tests/blimp_browser_test.h
@@ -7,6 +7,7 @@
 
 #include <memory>
 
+#include "base/synchronization/waitable_event.h"
 #include "content/public/test/browser_test_base.h"
 
 namespace base {
@@ -33,13 +34,17 @@ class BlimpBrowserTest : public content::BrowserTestBase {
   // exit.
   void QuitRunLoop();
 
+  // Tells RunUntilCompletion() to break and discontinue processing UI & IO
+  // thread MessageLoops.
+  void SignalCompletion();
+
  protected:
   BlimpBrowserTest();
   ~BlimpBrowserTest() override;
 
-  // Run an asynchronous test in a nested run loop. The caller should call
-  // QuitRunLoop() to notify that the test should finish.
-  void RunUntilQuit();
+  // Processes tasks in the UI and IO thread until SignalCompletion() is
+  // called.
+  void RunUntilCompletion();
 
   engine::BlimpEngineSession* GetEngineSession();
 
@@ -50,15 +55,20 @@ class BlimpBrowserTest : public content::BrowserTestBase {
 
   // content::BrowserTestBase implementation.
   void RunTestOnMainThreadLoop() override;
+  void SetUpCommandLine(base::CommandLine* command_line) override;
   void SetUpOnMainThread() override;
   void TearDownOnMainThread() override;
-  void SetUpCommandLine(base::CommandLine* command_line) override;
 
  private:
-  void OnGetEnginePort(uint16_t port);
+  // Receives the port number from an asynchronously connected socket.
+  // Calls SignalCompletion() when set.
+  void OnGetEnginePortCompletion(uint16_t port);
 
   uint16_t engine_port_;
-  std::unique_ptr<base::RunLoop> run_loop_;
+
+  // Used to signal the completion of asynchronous processing to
+  // RunUntilCompletion().
+  base::WaitableEvent completion_event_;
 
   DISALLOW_COPY_AND_ASSIGN(BlimpBrowserTest);
 };