Keep event page alive when there's some Pepper plugin on it.

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index b040d64223fe81a143daaedff660bad609e10dd2..7b3a51974a48f776a68b6d253e8539a673d41104 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -278,6 +278,11 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   virtual void AppCacheAccessed(const GURL& manifest_url,
                                 bool blocked_by_policy) {}
 
+  // These methods are invoked when a Pepper plugin instance is
+  // attached/detached in the page DOM.

[nasko, 2015/05/11 16:24:09]

The comment uses "attached/detached", but the name is Created/Deleted. Which one
is it? Can a pepper plugin instance be created and not attached to the DOM? If
yes, will this notification fire if that's the case?

[emaxx, 2015/05/18 15:06:29]

The notifications are only about Pepper instances appearing/disappearing in the
page DOM tree (though I don't think it's possible to create a Pepper instance
separate from any DOM tree).
Anyway, I've changed the wording to use "created"/"deleted" everywhere.

[nasko, 2015/05/19 14:11:45]

If this notification is about plugin being added to the DOM, while has already
been created, then it seems to me that it is better to rename the methods to
reflect reality instead of bring confusion.

[emaxx, 2015/05/19 17:33:40]

As far as I understand, no real loading is performed before the <embed> is added
to the DOM (Ben, please correct me if that's not true). So I don't think that
brings any confusion.

Also, the same naming style is already used in the existing members of the
RenderViewImpl class:
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/r...

+  virtual void PepperInstanceCreated() {}
+  virtual void PepperInstanceDeleted() {}
+
   // Notification that a plugin has crashed.
   // |plugin_pid| is the process ID identifying the plugin process. Note that
   // this ID is supplied by the renderer process, so should not be trusted.