Track where WebContents are created in order to better understand issue.

content/browser/web_contents/web_contents_impl.h

Index: content/browser/web_contents/web_contents_impl.h
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index 8fc964948f17bbee00780ce4c76a848101cf36fd..356a56ef87de5a7e4246a9333bbbd59761c14f38 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -11,6 +11,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/containers/scoped_ptr_hash_map.h"
+#include "base/debug/stack_trace.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
@@ -373,6 +374,7 @@ class CONTENT_EXPORT WebContentsImpl
   void HasManifest(const HasManifestCallback& callback) override;
   void ExitFullscreen() override;
   void ResumeLoadingCreatedWebContents() override;
+  base::debug::StackTrace stack_trace() override;
 #if defined(OS_ANDROID)
   void OnMediaSessionStateChanged();
   void ResumeMediaSession() override;
@@ -1329,6 +1331,9 @@ class CONTENT_EXPORT WebContentsImpl
 
   bool page_scale_factor_is_one_;
 
+  // Temporary to track down http://crbug.com/538612
+  base::debug::StackTrace stack_trace_;
+
   base::WeakPtrFactory<WebContentsImpl> loading_weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsImpl);