Add WebWidgetTestProxy.

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index daee7170916a6f19d73599d623067aec40007639..9e5623cddb1cacecbbfd5640b14bdf84979e414b 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -127,6 +127,20 @@ class CONTENT_EXPORT RenderWidget
                                       CompositorDependencies* compositor_deps,
                                       blink::WebLocalFrame* frame);
 
+  // Used by content_layouttest_support to hook into the creation of
+  // RenderWidgets.
+  using CreateRenderWidgetFunction =
+      RenderWidget* (*)(CompositorDependencies*,
+                        blink::WebPopupType,
+                        const blink::WebScreenInfo&,
+                        bool,
+                        bool,
+                        bool);
+  using RenderWidgetCreatedCallback = void (*)(RenderWidget*);

[Łukasz Anforowicz, 2016/08/11 17:19:28]

nit: Would it be more accurate to call this RenderWidgetInitedCallback? (or
"Initialized" if "Inited" is not a word :-P).

[lfg, 2016/08/11 19:49:39]

Done.

+  static void InstallCreateHook(
+      CreateRenderWidgetFunction create_render_widget,
+      RenderWidgetCreatedCallback render_widget_created_callback);
+
   // Closes a RenderWidget that was created by |CreateForFrame|.
   // TODO(avi): De-virtualize this once RenderViewImpl has-a RenderWidget.
   // https://crbug.com/545684