Force-generate a frame before the end of a layout test.

components/test_runner/web_test_runner.h

Index: components/test_runner/web_test_runner.h
diff --git a/components/test_runner/web_test_runner.h b/components/test_runner/web_test_runner.h
index b7efae1ed720dc663c4b96c03598c716f7d5688d..97acef95f9274efa35f43ae0fd6871f2b2600726 100644
--- a/components/test_runner/web_test_runner.h
+++ b/components/test_runner/web_test_runner.h
@@ -43,6 +43,9 @@ class WebTestRunner {
   // (i.e. by calling testRunner.dumpChildFramesAsText() from javascript).
   virtual bool IsRecursiveLayoutDumpRequested() = 0;
 
+  // Runs any pending animations on existing widgets.
+  virtual void RunPendingAnimations();
+
   // Dumps layout of |frame| using the mode requested by the current test
   // (i.e. text mode if testRunner.dumpAsText() was called from javascript).
   virtual std::string DumpLayout(blink::WebLocalFrame* frame) = 0;