Move DumpBackForwardLists out of WebTestProxyBase.

Iterating over all known test windows can be moved out of
web_test_proxy_base.cc and into blink_test_runner.cc.  This helps
minimize the amount of code in WebTestProxyBase (which should hopefully
be just a passive holder of WebView, WebViewTestClient, etc. - all logic
should be implemented inside WebViewTestClient and [future]
WebWidgetTestClient).

BUG=595089

Review URL: https://codereview.chromium.org/1886103002

Cr-Commit-Position: refs/heads/master@{#387465}
diff --git a/components/test_runner/web_test_interfaces.h b/components/test_runner/web_test_interfaces.h
index 0c12ef6..29942c1 100644
--- a/components/test_runner/web_test_interfaces.h
+++ b/components/test_runner/web_test_interfaces.h
@@ -5,6 +5,8 @@
 #ifndef COMPONENTS_TEST_RUNNER_WEB_TEST_INTERFACES_H_
 #define COMPONENTS_TEST_RUNNER_WEB_TEST_INTERFACES_H_
 
+#include <vector>
+
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "components/test_runner/test_runner_export.h"
@@ -79,6 +81,9 @@
   scoped_ptr<WebViewTestClient> CreateWebViewTestClient(
       WebTestProxyBase* web_test_proxy_base);
 
+  // Gets a list of currently opened windows created by the current test.
+  std::vector<blink::WebView*> GetWindowList();
+
  private:
   scoped_ptr<TestInterfaces> interfaces_;