Allow use of container cbegin() and cend() methods, plus sample uses.

This also fixes a small bug in the histogram recording of TabStripModelStatsRecorder::ActiveTabChanged() I spotted while doing this.

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/1675483002

Cr-Commit-Position: refs/heads/master@{#374827}

chrome/browser/ui/tabs/tab_strip_model_stats_recorder.cc

@@ -168,14 +168,14 @@ void TabStripModelStatsRecorder::ActiveTabChanged(
   // A UMA Histogram must be bounded by some number.
   // We chose 64 as our bound as 99.5% of the users open <64 tabs.
   const int kMaxTabHistory = 64;
-  auto it = std::find(active_tab_history_.begin(), active_tab_history_.end(),
+  auto it = std::find(active_tab_history_.cbegin(), active_tab_history_.cend(),
                       new_contents);
-  int age = it != active_tab_history_.end() ? (it - active_tab_history_.begin())
-                                            : (kMaxTabHistory - 1);
+  int age = (it != active_tab_history_.cend()) ?
+      (it - active_tab_history_.cbegin()) : (kMaxTabHistory - 1);
   if (was_inactive) {
     UMA_HISTOGRAM_ENUMERATION(
         "Tabs.StateTransfer.NumberOfOtherTabsActivatedBeforeMadeActive",
-        std::min(age, kMaxTabHistory), kMaxTabHistory);
+        std::min(age, kMaxTabHistory - 1), kMaxTabHistory);
   }
 
   active_tab_history_.insert(active_tab_history_.begin(), new_contents);

chrome/browser/ui/views/toolbar/browser_actions_container.cc

@@ -588,11 +588,10 @@ void BrowserActionsContainer::WriteDragDataForView(View* sender,
   toolbar_actions_bar_->OnDragStarted();
   DCHECK(data);
 
-  ToolbarActionViews::iterator iter = std::find(toolbar_action_views_.begin(),
-                                                toolbar_action_views_.end(),
-                                                sender);
-  DCHECK(iter != toolbar_action_views_.end());
-  ToolbarActionViewController* view_controller = (*iter)->view_controller();
+  auto it = std::find(toolbar_action_views_.cbegin(),
+                      toolbar_action_views_.cend(), sender);
+  DCHECK(it != toolbar_action_views_.cend());
+  ToolbarActionViewController* view_controller = (*it)->view_controller();
   gfx::Size size(ToolbarActionsBar::IconWidth(false),
                  ToolbarActionsBar::IconHeight());
   drag_utils::SetDragImageOnDataObject(
@@ -601,7 +600,7 @@ void BrowserActionsContainer::WriteDragDataForView(View* sender,
       data);
   // Fill in the remaining info.
   BrowserActionDragData drag_data(view_controller->GetId(),
-                                  iter - toolbar_action_views_.begin());
+                                  it - toolbar_action_views_.cbegin());
   drag_data.Write(browser_->profile(), data);
 }
 

styleguide/c++/c++11.html

@@ -357,13 +357,10 @@ Note that &lt;algorithm&gt; contains a range-based <code>move</code> method.  Th
 <tr>
 <td>Begin and End Non-Member Functions</td>
 <td><code>std::begin()</code> and <code>std::end()</code></td>
-<td>Allows use of free functions on any container, including
-fixed-size arrays</td>
-<td><a href="http://en.cppreference.com/w/cpp/iterator/begin">
-std::begin</a> and
-<a href="http://en.cppreference.com/w/cpp/iterator/end">
-std::end</a></td>
-<td>Useful for fixed-size arrays. <a href="https://groups.google.com/a/chromium.org/d/topic/cxx/5iFNE8P5qT4/discussion">Discussion thread</a></td>
+<td>Allows use of free functions on any container, including fixed-size arrays</td>
+<td><a href="http://en.cppreference.com/w/cpp/iterator/begin">std::begin</a> and <a href="http://en.cppreference.com/w/cpp/iterator/end">std::end</a></td>
+<td>Useful for fixed-size arrays. <a href="https://groups.google.com/a/chromium.org/d/topic/cxx/5iFNE8P5qT4/discussion">Discussion thread</a><br>
+Note that non-member <code>cbegin()</code> and <code>cend()</code> are not available until C++14.</td>
 </tr>
 
 <tr>
@@ -374,6 +371,14 @@ std::end</a></td>
 <td>Usage should be rare. <a href='https://groups.google.com/a/chromium.org/forum/#!topic/cxx/vCxo4tZNd_M'>Discussion thread</a></td>
 </tr>
 
+<tr>
+<td>Constant Iterator Methods on Containers</td>
+<td><code>std::vector::cbegin()</code>, <code>std::vector::cend()</code></td>
+<td>Allows more widespread use of <code>const_iterator</code></td>
+<td>E.g. <a href="http://en.cppreference.com/w/cpp/container/vector/begin">std::vector::cbegin<a> and <a href="http://en.cppreference.com/w/cpp/container/vector/end">std::vector::cend<a></td>
+<td>Applies to all containers, not just <code>vector</code>.  Consider using <code>const_iterator</code> over <code>iterator</code> where possible for the same reason as using <code>const</code> variables and functions where possible; see Effective Modern C++ item 13 for motivation.  <a href="https://groups.google.com/a/chromium.org/d/topic/cxx/cS83F_buqLM/discussion">Discussion thread</a></td>
+</tr>
+
 <tr>
 <td>Containers containing movable types</td>
 <td><code>vector&lt;scoped_ptr&gt;</code></td>
@@ -845,14 +850,6 @@ the <code>&lt;complex&gt;</code> library.</td>
 <td></td>
 </tr>
 
-<tr>
-<td>Constant Iterator Methods on Containers</td>
-<td><code>std::vector::cbegin()</code> and <code>std::vector::cend()</code></td>
-<td>Enforces iteration methods that don't change container contents</td>
-<td><a href="http://en.cppreference.com/w/cpp/container/vector/begin">std::vector::cbegin<a></td>
-<td>This applies to all containers, std::vector is just an example. <a href="https://groups.google.com/a/chromium.org/d/topic/cxx/cS83F_buqLM/discussion">Discussion thread</a></td>
-</tr>
-
 <tr>
 <td>Container Compaction Functions</td>
 <td><code>std::vector::shrink_to_fit()</code>,

ui/views/view_unittest.cc

@@ -3505,12 +3505,8 @@ TEST_F(ViewTest, GetViewByID) {
   View::Views views;
   v1.GetViewsInGroup(kGroup, &views);
   EXPECT_EQ(2U, views.size());
-
-  View::Views::const_iterator i(std::find(views.begin(), views.end(), &v3));
-  EXPECT_NE(views.end(), i);
-
-  i = std::find(views.begin(), views.end(), &v4);
-  EXPECT_NE(views.end(), i);
+  EXPECT_NE(views.cend(), std::find(views.cbegin(), views.cend(), &v3));
+  EXPECT_NE(views.cend(), std::find(views.cbegin(), views.cend(), &v4));
 }
 
 TEST_F(ViewTest, AddExistingChild) {

ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc

@@ -68,11 +68,9 @@ class WMStateWaiter : public X11PropertyChangeWaiter {
   bool ShouldKeepOnWaiting(const ui::PlatformEvent& event) override {
     std::vector<Atom> hints;
     if (ui::GetAtomArrayProperty(xwindow(), "_NET_WM_STATE", &hints)) {
-      std::vector<Atom>::iterator it = std::find(
-          hints.begin(),
-          hints.end(),
+      auto it = std::find(hints.cbegin(), hints.cend(),
                           atom_cache_->GetAtom(hint_));
-      bool hint_set = (it != hints.end());
+      bool hint_set = (it != hints.cend());
       return hint_set != wait_till_set_;
     }
     return true;

ui/views/widget/desktop_aura/x11_topmost_window_finder_interactive_uitest.cc

@@ -55,11 +55,9 @@ class MinimizeWaiter : public X11PropertyChangeWaiter {
   bool ShouldKeepOnWaiting(const ui::PlatformEvent& event) override {
     std::vector<Atom> wm_states;
     if (ui::GetAtomArrayProperty(xwindow(), "_NET_WM_STATE", &wm_states)) {
-      std::vector<Atom>::iterator it = std::find(
-          wm_states.begin(),
-          wm_states.end(),
+      auto it = std::find(wm_states.cbegin(), wm_states.cend(),
                           atom_cache_->GetAtom("_NET_WM_STATE_HIDDEN"));
-      return it == wm_states.end();
+      return it == wm_states.cend();
     }
     return true;
   }
@@ -97,9 +95,8 @@ class StackingClientListWaiter : public X11PropertyChangeWaiter {
     std::vector<XID> stack;
     ui::GetXWindowStack(ui::GetX11RootWindow(), &stack);
     for (size_t i = 0; i < expected_windows_.size(); ++i) {
-      std::vector<XID>::iterator it = std::find(
-          stack.begin(), stack.end(), expected_windows_[i]);
-      if (it == stack.end())
+      auto it = std::find(stack.cbegin(), stack.cend(), expected_windows_[i]);
+      if (it == stack.cend())
         return true;
     }
     return false;