Add histogram Omnibox.FocusToEditTime for time in milliseconds between a user focus and edit.

chrome/browser/ui/omnibox/omnibox_edit_model.cc

Index: chrome/browser/ui/omnibox/omnibox_edit_model.cc
===================================================================
--- chrome/browser/ui/omnibox/omnibox_edit_model.cc	(revision 209999)
+++ chrome/browser/ui/omnibox/omnibox_edit_model.cc	(working copy)
@@ -93,6 +93,10 @@
 // in the EnteredKeywordModeMethod enum which is defined in the .h file.
 const char kEnteredKeywordModeHistogram[] = "Omnibox.EnteredKeywordMode";
 
+// Histogram name which counts the number of milliseconds a user takes
+// between focusing and editing the omnibox.
+const char kFocusToEditHistogram[] = "Omnibox.FocusToEdit";
+
 }  // namespace
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -414,6 +418,9 @@
   if (user_input_in_progress_) {
     time_user_first_modified_omnibox_ = base::TimeTicks::Now();
     content::RecordAction(content::UserMetricsAction("OmniboxInputInProgress"));
+    UMA_HISTOGRAM_COUNTS(kFocusToEditHistogram,

[Mark P, 2013/07/08 21:58:30]

COUNTS is not the right type of histogram for times.

[H Fung, 2013/07/09 01:09:55]

I switched to UMA_HISTOGRAM_TIMES but I guess the histogram values are
exponential so the boundaries aren't easily calculated.

+                         (time_user_first_modified_omnibox_ -
+                          time_user_last_focused_on_omnibox_).InMilliseconds());

[Mark P, 2013/07/08 21:58:30]

You might want to DCHECK that time_user_last_focused_on_omnibox_ has been set
and also is less than (or equal) to time_user_first_modified_omnibox_.

[H Fung, 2013/07/09 01:09:55]

I do a manual check that the time has been set now, and added a DCHECK to verify
the time was set sometime in the past.

     autocomplete_controller()->ResetSession();
   }
   controller_->OnInputInProgress(in_progress);
@@ -802,6 +809,8 @@
 }
 
 void OmniboxEditModel::OnSetFocus(bool control_down) {
+  time_user_last_focused_on_omnibox_ = base::TimeTicks::Now();
+
   // If the omnibox lost focus while the caret was hidden and then regained
   // focus, OnSetFocus() is called and should restore visibility. Note that
   // focus can be regained without an accompanying call to