Add support for distilling current WebContents

chrome/browser/ui/tab_helpers.cc

Index: chrome/browser/ui/tab_helpers.cc
diff --git a/chrome/browser/ui/tab_helpers.cc b/chrome/browser/ui/tab_helpers.cc
index 05924e3767b77f4e4895d89d4a3ee6383fd11f32..5bdbb2f5a39d135717d3055a0315fd10d97b6dfd 100644
--- a/chrome/browser/ui/tab_helpers.cc
+++ b/chrome/browser/ui/tab_helpers.cc
@@ -29,6 +29,7 @@
 #include "chrome/common/chrome_switches.h"
 #include "components/autofill/content/browser/content_autofill_driver.h"
 #include "components/autofill/core/browser/autofill_manager.h"
+#include "components/dom_distiller/content/web_contents_main_frame_observer.h"
 #include "components/password_manager/core/browser/password_manager.h"
 #include "content/public/browser/web_contents.h"
 #include "extensions/browser/view_type_utils.h"
@@ -191,6 +192,12 @@ void TabHelpers::AttachTabHelpers(WebContents* web_contents) {
 #endif  // defined(ENABLE_FULL_PRINTING)
 #endif  // defined(ENABLE_PRINTING) && !defined(OS_ANDROID)
 
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableDomDistiller)) {
+    dom_distiller::WebContentsMainFrameObserver::CreateForWebContents(

[sky, 2014/05/20 20:59:45]

Why do we need to do this here? Can't you install whatever is needed when the
menu item is clicked?

[nyquist, 2014/05/20 21:03:28]

The WebContentsMainFrameObserver is only there to track whether the
WebContentsObservers of the given |web_contents| have gotten a call to
DocumentLoadedInFrame for the main frame. Adding it at the time of when you
click the menu item would be too late, as the event has most probably already
been triggered. Say you go to a page, click the menu item, and then add the
observer; chances are the page has already (at least mostly) loaded.

After talking to jam@ I realized that putting this state tracking in //content
was not encouraged, if it was possible to do it in //chrome.

[sky, 2014/05/20 23:25:20]

Can't you determine what you need at the time you need it rather than making
everything get more expensive in anticipation of using something?

[nyquist, 2014/05/20 23:28:11]

That would be great, but I could not find any place where this state is already
stored. In WebContents / WebContentsImpl, the events are just forwarded to the
observers. Any thoughts as to where this could already be?

+        web_contents);
+  }
+
 #if defined(ENABLE_ONE_CLICK_SIGNIN)
   // If this is not an incognito window, setup to handle one-click login.
   // We don't want to check that the profile is already connected at this time