[DO NOT COMMIT] Remove chrome::NOTIFICATION_RETARGETING

content/test/web_contents_observer_sanity_checker.cc

Index: content/test/web_contents_observer_sanity_checker.cc
diff --git a/content/test/web_contents_observer_sanity_checker.cc b/content/test/web_contents_observer_sanity_checker.cc
index 1d85380fc7827c17a154e04b50c26f26e3e561ce..f3a72cb2dede13ee00f41235fa4198622488188b 100644
--- a/content/test/web_contents_observer_sanity_checker.cc
+++ b/content/test/web_contents_observer_sanity_checker.cc
@@ -4,6 +4,7 @@
 
 #include "content/test/web_contents_observer_sanity_checker.h"
 
+#include "base/debug/stack_trace.h"
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
@@ -23,6 +24,10 @@ namespace {
 const char kWebContentsObserverSanityCheckerKey[] =
     "WebContentsObserverSanityChecker";
 
+// Set this variable to true to collect stack traces on observer method calls
+// so duplicate ones can be easily debugged.
+static bool g_collect_stack_traces = true;
+
 GlobalRoutingID GetRoutingPair(RenderFrameHost* host) {
   if (!host)
     return GlobalRoutingID(0, 0);
@@ -282,6 +287,16 @@ void WebContentsObserverSanityChecker::DidOpenRequestedURL(
     WindowOpenDisposition disposition,
     ui::PageTransition transition) {
   AssertRenderFrameExists(source_render_frame_host);
+
+  std::string trace;
+  if (g_collect_stack_traces) {
+    base::debug::StackTrace stack_trace;
+    trace = stack_trace.ToString();
+  }
+
+  bool did_not_exist = created_web_contents_.insert(std::make_pair(new_contents, trace)).second;
+  CHECK(did_not_exist) << "A WebContents was created for the same address as previously "
+                          "created one. The original one was allocated by:\n" << trace;
 }
 
 void WebContentsObserverSanityChecker::MediaStartedPlaying(