Add histogram for how tab closing time. Did some cleanup along the way.

chrome/browser/renderer_host/render_view_host.h

Index: chrome/browser/renderer_host/render_view_host.h
===================================================================
--- chrome/browser/renderer_host/render_view_host.h	(revision 28997)
+++ chrome/browser/renderer_host/render_view_host.h	(working copy)
@@ -639,11 +639,6 @@
   // must return to the renderer to unblock it.
   IPC::Message* run_modal_reply_msg_;
 
-  // Set to true when there is an active "before unload" dialog.  When true,
-  // we've forced the throbber to start in Navigate, and we need to remember to
-  // turn it off in JavaScriptMessageBoxClosed if the navigation is canceled.
-  bool is_showing_before_unload_dialog_;

[tony, 2009/10/14 23:20:06]

Nit: Can you explain why this moved in the change description?

[jam, 2009/10/14 23:31:11]

Oh, that doesn't fix any bug.  It's just convenient so that the flag is in
tab_contents, which is where I want to do the time related code.  I needed a
flag there to know when a before unload dialog closes, to reset the time.  Added
a comment to the description.

-
   // Set to true when there is a pending ViewMsg_ShouldClose message pending.
   // This ensures we don't spam the renderer many times to close. When true,
   // the value of unload_ack_is_for_cross_site_transition_ indicates which type