Migrate MediaStream test code from content/shell/renderer/ to content/test/.

content/public/test/layouttest_support.h

Index: content/public/test/layouttest_support.h
diff --git a/content/public/test/layouttest_support.h b/content/public/test/layouttest_support.h
index ed490ec5a12363a4d89b66521013791e92af7eb1..5ae7396e7cc4c1a1d0ff463ee7f7498b0b7ee3d4 100644
--- a/content/public/test/layouttest_support.h
+++ b/content/public/test/layouttest_support.h
@@ -64,6 +64,9 @@ void EnableAutoResizeMode(RenderView* render_view,
 void DisableAutoResizeMode(RenderView* render_view,
                            const WebKit::WebSize& new_size);
 
+// Forces the |render_view| to use mock media streams.
+void UseMockMediaStreams(RenderView* render_view);
+
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_TEST_LAYOUTTEST_SUPPORT_H_