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..bae8ef296ba7370eeb31739a3278fc6f6140b2a0 100644
--- a/content/shell/shell.h
+++ b/content/shell/shell.h
@@ -13,6 +13,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/string_piece.h"
 #include "content/public/browser/web_contents_delegate.h"
+#include "content/public/browser/web_contents_observer.h"
 #include "ui/gfx/native_widget_types.h"
 
 #if defined(OS_LINUX)
@@ -31,7 +32,8 @@ class SiteInstance;
 
 // This represents one window of the Content Shell, i.e. all the UI including
 // buttons and url bar, as well as the web content area.
-class Shell : public WebContentsDelegate {
+class Shell : public WebContentsDelegate,
+              public WebContentsObserver {
  public:
   virtual ~Shell();
 
@@ -71,7 +73,7 @@ class Shell : public WebContentsDelegate {
     STOP_BUTTON
   };
 
-  Shell();
+  explicit Shell(TabContents* tab_contents);
 
   // Helper to create a new Shell given a newly created TabContents.
   static Shell* CreateShell(TabContents* tab_contents);
@@ -107,6 +109,11 @@ class Shell : public WebContentsDelegate {
   virtual void UpdatePreferredSize(WebContents* source,
                                    const gfx::Size& pref_size) OVERRIDE;
 
+  // content::WebContentsObserver
+  virtual void DidFinishLoad(int64 frame_id,
+                             const GURL& validated_url,
+                             bool is_main_frame) OVERRIDE;
+
 #if defined(OS_WIN)
   static ATOM RegisterWindowClass();
   static LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);