Multi-tab selection for Linux.

chrome/browser/tabs/tab_strip_model_observer.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_TABS_TAB_STRIP_MODEL_OBSERVER_H_
 #define CHROME_BROWSER_TABS_TAB_STRIP_MODEL_OBSERVER_H_
 #pragma once
 
+#include <vector>
+
 class TabContentsWrapper;
 class TabStripModel;
 
 ////////////////////////////////////////////////////////////////////////////////
 //
 // TabStripModelObserver
 //
 //  Objects implement this interface when they wish to be notified of changes
 //  to the TabStripModel.
 //
@@ skipping 45 matching lines @@
   // Sent when the selection changes. The previously selected tab is identified
   // by |old_contents| and the newly selected tab by |new_contents|. |index| is
   // the index of |new_contents|. When using multiple selection this may be sent
   // even when the active tab has not changed. For example, if the selection is
   // extended this method is invoked to inform observers the selection has
   // changed, but |old_contents| and |new_contents| are the same.  If you only
   // care about when the active tab changes, check for when |old_contents|
   // differs from |new_contents|. |user_gesture| specifies whether or not this
   // was done by a user input event (e.g. clicking on a tab, keystroke) or as a
   // side-effect of some other function.
-  //
-  // TODO(dpapad): Add TabSelectionChanged method for when the selected tabs
-  // change.
   virtual void ActiveTabChanged(TabContentsWrapper* old_contents,
                                 TabContentsWrapper* new_contents,
                                 int index,
                                 bool user_gesture);
 
+  // Sent when the selection changes. |previously_selected| and
+  // |currently_selected| contain the indices of the tabs that were previously
+  // and currently selected respectively.
+  virtual void TabSelectionChanged(const std::vector<int>& previously_selected,

[sky, 2011/06/01 20:56:04]

Add test coverage of this.
Also, it seems like you don't always invoke this when the selected indices
change. The case I think you don't send out notification are add/remove. For
example, if you add/remove tabs, the selection in terms of indices changes.

[dpapad, 2011/06/02 00:28:22]

Yes, currently TabSelectionChanged() is called from ActivateTabAt(),
ExtendSelectionTo(), ToggleSelectionAt(), AddSelectionFromAnchorTo() and
SetSelectionFromModel(). It is intentionally not called from
InsertTabContentsAt() and CloseTabContentsAt(), for 2 reasons, 1st) These events
seem to be handled fine by existing callbacks (in terms of repainting) and 2nd)
to avoid sending indices of tabs that no longer exist (as noted in one of your
comments). 
I see two approaches
1) Add some more comments in TabSelectionChanged explaining that it is not
always fired when the selection changes.
2) Call TabSelectionChanged() from InsertTabContentsAt() and
CloseTabContentsAt() too and find out how to deal with differences in model_ and
tab_data_ in TabStripGtk (maybe send the TabContentsWrapper* instead of the
indices?).

[sky, 2011/06/02 16:07:14]

You're right on 1. My intention with the two methods is the following:
. ActiveTabChanged: only sent when the active tab changes. Currently it isn't
and most implementations check before doing anything. At the time I added
multi-selection I went this route, rather than a new method, as we weren't sure
if we were going to keep the feature.
. TabSelectionChanged: sent when the selection changes, but not necessarily the
active tab, and not when tabs are inserted/removed.

Since TabSelectionChanged will be sent when ActiveTabChanged is sent now that
means it should be enough for the TabStrip implementations to only listen to
TabSelectionChanged.

I think it would be best to separate out the model changes into a patch doing
the following:
. Only send ActiveTabChanged when the active tab really changes. You'll then be
able to remove a bunch of checks I added. See
http://src.chromium.org/viewvc/chrome?view=rev&revision=76619 .
. Add TabSelectionChanged and change the places that care about any selection
change to override TabSelectionChanged instead of ActiveTabChanged.
. For TabSelectionChanged, make it take const TabStripSelectionModel& as the
only argument. It'll be the selection before the change. If folks care about the
new selection, they can query the model.
. Add/update tests.

+                                   const std::vector<int>& currently_selected);
+
   // The specified TabContents at |from_index| was moved to |to_index|.
   virtual void TabMoved(TabContentsWrapper* contents,
                         int from_index,
                         int to_index);
 
   // The specified TabContents at |index| changed in some way. |contents| may
   // be an entirely different object and the old value is no longer available
   // by the time this message is delivered.
   //
   // See TabChangeType for a description of |change_type|.
@@ skipping 35 matching lines @@
 
   // Invoked when an active/selected tab at |index| is selected again (ie - the
   // active/foreground tab is clicked).
   virtual void ActiveTabClicked(int index);
 
  protected:
   virtual ~TabStripModelObserver() {}
 };
 
 #endif  // CHROME_BROWSER_TABS_TAB_STRIP_MODEL_OBSERVER_H_