Fix headless_browsertests failures with PlzNavigate.

headless/lib/embedder_mojo_browsertest.cc

Index: headless/lib/embedder_mojo_browsertest.cc
diff --git a/headless/lib/embedder_mojo_browsertest.cc b/headless/lib/embedder_mojo_browsertest.cc
index 51cc2cb63ff1dac58997bf6ab078f63ce90ed5e7..17ce6ebac217e752b08934b8abdb65412ef1551d 100644
--- a/headless/lib/embedder_mojo_browsertest.cc
+++ b/headless/lib/embedder_mojo_browsertest.cc
@@ -5,6 +5,7 @@
 #include <memory>
 #include "base/optional.h"
 #include "base/path_service.h"
+#include "base/run_loop.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_restrictions.h"
@@ -225,12 +226,16 @@ class HttpDisabledByDefaultWhenMojoBindingsUsed : public EmbedderMojoTest,
   }
 
   void RunMojoTest() override {
+    base::RunLoop run_loop;
     devtools_client_->GetNetwork()->AddObserver(this);
-    devtools_client_->GetNetwork()->Enable();
-  }
-
-  GURL GetInitialUrl() const override {
-    return embedded_test_server()->GetURL("/page_one.html");
+    devtools_client_->GetNetwork()->Enable(run_loop.QuitClosure());

[Sami, 2017/02/27 11:46:19]

nit: It might make sense to add a helper method to do this to cut down on the
repetition.

[jam, 2017/02/27 15:18:18]

The issue is that the module that Enable is called on differs (i.e. GetNetwork,
GetPage), so the code sharing would have to be an object that stores state and
is called a few times, all to save a few lines.

[Sami, 2017/02/27 16:22:53]

Ah, I was just thinking of two helpers like EnablePageDomainSynchronously() and
EnableNetworkDomainSynchronously(). WDYT?

[jam, 2017/02/27 16:29:43]

The issue is we'd need more as other test use other devtools modules.

IMO I didn't think it's necessary to have this helper; if you disagree and want
it please let me know and I'll add it.

[Sami, 2017/02/27 16:36:39]

Fair enough, it was just a small nit. We'll rethink this if it starts to become
annoying.

+    base::MessageLoop::ScopedNestableTaskAllower nest_loop(
+        base::MessageLoop::current());
+    run_loop.Run();
+    devtools_client_->GetPage()->AddObserver(this);
+    devtools_client_->GetPage()->Enable();
+    devtools_client_->GetPage()->Navigate(
+        embedded_test_server()->GetURL("/page_one.html").spec());
   }
 
   void ReturnTestResult(const std::string& result) override {