Explicitly initialize secondary renderers for layout tests.

content/shell/browser/layout_test/blink_test_controller.h

Index: content/shell/browser/layout_test/blink_test_controller.h
diff --git a/content/shell/browser/layout_test/blink_test_controller.h b/content/shell/browser/layout_test/blink_test_controller.h
index 602438c737eb85d17f81cbd67cdd72763d5eaddb..ea352288b4f07109ce0b8606bf0950941db8ec94 100644
--- a/content/shell/browser/layout_test/blink_test_controller.h
+++ b/content/shell/browser/layout_test/blink_test_controller.h
@@ -8,6 +8,7 @@
 #include <map>
 #include <memory>
 #include <ostream>
+#include <set>
 #include <string>
 
 #include "base/cancelable_callback.h"
@@ -133,6 +134,11 @@ class BlinkTestController : public base::NonThreadSafe,
   // True if the controller was reset successfully.
   bool ResetAfterLayoutTest();
 
+  // Makes sure that the potentially new renderer associated with |frame| is 1)
+  // initialized for the test, 2) kept-up-to-date wrt test flags and 3)
+  // monitored for crashes.
+  void HandleNewRenderFrameHost(RenderFrameHost* frame);
+
   void SetTempPath(const base::FilePath& temp_path);
   void RendererUnresponsive();
   void OverrideWebkitPrefs(WebPreferences* prefs);
@@ -184,8 +190,6 @@ class BlinkTestController : public base::NonThreadSafe,
   static BlinkTestController* instance_;
 
   void DiscardMainWindow();
-  void HandleNewRenderFrameHost(
-      RenderFrameHost* frame_representing_target_process);
 
   // Message handlers.
   void OnAudioDump(const std::vector<unsigned char>& audio_dump);
@@ -266,6 +270,8 @@ class BlinkTestController : public base::NonThreadSafe,
   // Renderer processes are observed to detect crashes.
   ScopedObserver<RenderProcessHost, RenderProcessHostObserver>
       render_process_host_observer_;
+  std::set<RenderProcessHost*> all_observed_render_process_hosts_;

[Łukasz Anforowicz, 2016/04/15 20:15:29]

This field is somewhat redundant - render_process_host_observer_ already
contains the same set of RenderProcessHosts, but it is locked inside
ScopedObserver.  I guess I could try to add an accessor to ScopedObserver, but
that would mean pushback from //base owners unless I find 2-3 other cases that
would need an accessor...  Path of least resistance...

+  std::set<RenderProcessHost*> main_window_render_process_hosts_;
 
   // Changes reported by OnLayoutTestRuntimeFlagsChanged that have accumulated
   // since PrepareForLayoutTest (i.e. changes that need to be send to a fresh