Makes the touch tabstrip scroll so that tabs opened in the background

chrome/browser/ui/views/tabs/touch_tab_strip_layout.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/views/tabs/touch_tab_strip_layout.h"
 
 #include <stdio.h>
 
 #include "base/logging.h"
 #include "base/string_number_conversions.h"
@@ skipping 90 matching lines @@
   if (!requires_stacking() || normal_tab_count() <= 1) {
     ResetToIdealState();
     return;
   }
   int active_x = (index + 1 == tab_count()) ?
       width_ - size_.width() : ideal_x(index + 1);
   SetIdealBoundsAt(active_index(), ConstrainActiveX(active_x));
   LayoutByTabOffsetAfter(active_index());
   LayoutByTabOffsetBefore(active_index());
   AdjustStackedTabs();
+
+  if ((add_types & kAddTypeActive) == 0)
+    MakeVisible(index);
 }
 
 void TouchTabStripLayout::RemoveTab(int index, int start_x, int old_x) {
   if (index == active_index_)
     active_index_ = std::min(active_index_, tab_count() - 1);
   else if (index < active_index_)
     active_index_--;
   bool removed_mini_tab = index < mini_tab_count_;
   if (removed_mini_tab) {
     mini_tab_count_--;
@@ skipping 100 matching lines @@
       SetIdealBoundsAt(index, x_ + stacked_padding);
       LayoutByTabOffsetAfter(index);
       LayoutByTabOffsetBefore(index);
       index--;
     } while (index >= mini_tab_count_ && ideal_x(mini_tab_count_) != x_ &&
              ideal_x(tab_count() - 1) != width_ - size_.width());
   }
   AdjustStackedTabs();
 }
 
+void TouchTabStripLayout::MakeVisible(int index) {
+  // Currently no need to support tabs openning before |index| visible.
+  if (index <= active_index() || !requires_stacking() || !IsStacked(index))
+    return;
+
+  int ideal_delta = width_for_count(index - active_index()) + padding_;
+  if (ideal_x(index) - ideal_x(active_index()) == ideal_delta)
+    return;
+
+  // First push active index as far to the left as it'll go.
+  int active_x = std::max(GetMinX(active_index()),
+                          std::min(ideal_x(index) - ideal_delta,
+                                   ideal_x(active_index())));
+  SetIdealBoundsAt(active_index(), active_x);
+  LayoutUsingCurrentBefore(active_index());
+  LayoutUsingCurrentAfter(active_index());
+  AdjustStackedTabs();
+  if (ideal_x(index) - ideal_x(active_index()) == ideal_delta)
+    return;
+
+  // If we get here active_index() is left aligned. Push |index| as far to
+  // the right as possible.
+  int x = std::min(GetMaxX(index), active_x + ideal_delta);
+  SetIdealBoundsAt(index, x);
+  LayoutByTabOffsetAfter(index);
+  for (int next_x = x, i = index - 1; i > active_index(); --i) {
+    next_x = std::max(GetMinXCompressed(i), next_x - tab_offset());
+    SetIdealBoundsAt(i, next_x);
+  }
+  LayoutUsingCurrentAfter(active_index());
+  AdjustStackedTabs();
+}
+
 int TouchTabStripLayout::ConstrainActiveX(int x) const {
   return std::min(GetMaxX(active_index()),
                   std::max(GetMinX(active_index()), x));
 }
 
 void TouchTabStripLayout::SetActiveBoundsAndLayoutFromActiveTab() {
   int x = ConstrainActiveX(ideal_x(active_index()));
   SetIdealBoundsAt(active_index(), x);
   LayoutUsingCurrentBefore(active_index());
   LayoutUsingCurrentAfter(active_index());
@@ skipping 156 matching lines @@
 }
 
 int TouchTabStripLayout::GetMinXCompressed(int index) const {
   DCHECK_GT(index, active_index());
   return std::max(
       width_ - width_for_count(tab_count() - index),
       ideal_x(active_index()) +
           stacked_padding_for_count(index - active_index()));
 
 }