Add abstractions that let embedders drive tests of WebContents.

content/browser/renderer_host/test_render_view_host.h

Index: content/browser/renderer_host/test_render_view_host.h
diff --git a/content/browser/renderer_host/test_render_view_host.h b/content/browser/renderer_host/test_render_view_host.h
index 298761e323d553ddf7b532871793e68da418a867..2803e538cf2e1f271d580512bb421be0c3da55d7 100644
--- a/content/browser/renderer_host/test_render_view_host.h
+++ b/content/browser/renderer_host/test_render_view_host.h
@@ -19,20 +19,19 @@
 // NavigationController, and other layers above that without running an actual
 // renderer process.
 //
-// To use, derive your test base class from RenderViewHostTestHarness.
+// To use, derive your test base class from RenderViewHostImplTestHarness.
 
-namespace content {
-class SiteInstance;
-}
+class TestTabContents;
+struct ViewHostMsg_FrameNavigate_Params;
 
 namespace gfx {
 class Rect;
 }
 
-struct ViewHostMsg_FrameNavigate_Params;
-
 namespace content {
 
+class SiteInstance;
+
 // Utility function to initialize ViewHostMsg_NavigateParams_Params
 // with given |page_id|, |url| and |transition_type|.
 void InitNavigateParams(ViewHostMsg_FrameNavigate_Params* params,
@@ -310,6 +309,7 @@ class RenderViewHostImplTestHarness : public RenderViewHostTestHarness {
   TestRenderViewHost* test_rvh();
   TestRenderViewHost* pending_test_rvh();
   TestRenderViewHost* active_test_rvh();
+  TestTabContents* contents();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(RenderViewHostImplTestHarness);