Add option --dump-render-tree to content_shell to dump the render tree as text.

content/shell/shell.h

Index: content/shell/shell.h
diff --git a/content/shell/shell.h b/content/shell/shell.h
index c4b09f7911d04640088ce6011eb46499823a7c69..d88cec3be9a61c744158f9276cfad754a9a669ca 100644
--- a/content/shell/shell.h
+++ b/content/shell/shell.h
@@ -41,6 +41,8 @@ class Shell : public WebContentsDelegate {
   void Stop();
   void UpdateNavigationControls();
 
+  void SetDumpAsText(bool dump_as_text);
+
   // Do one time initialization at application startup.
   static void PlatformInitialize();
 
@@ -99,6 +101,7 @@ class Shell : public WebContentsDelegate {
 
   // content::WebContentsDelegate
   virtual void LoadingStateChanged(WebContents* source) OVERRIDE;
+  virtual void DidFinishLoad(WebContents* source) OVERRIDE;
   virtual void WebContentsCreated(WebContents* source_contents,
                                   int64 source_frame_id,
                                   const GURL& target_url,
@@ -151,6 +154,9 @@ class Shell : public WebContentsDelegate {
   // A container of all the open windows. We use a vector so we can keep track
   // of ordering.
   static std::vector<Shell*> windows_;
+
+  // True if we should dump the page as text once it finished loading.
+  bool dump_as_text_;
 };
 
 }  // namespace content