Make Aura and compositor stacking methods more intuitive.

ui/gfx/compositor/layer.cc

 // 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.
 
 #include "ui/gfx/compositor/layer.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 117 matching lines @@
     return;  // Already in front.
   StackAbove(child, children_.back());
 
   SetNeedsToRecomputeHole();
 }
 
 void Layer::StackAbove(Layer* child, Layer* other) {
   DCHECK_NE(child, other);
   DCHECK_EQ(this, child->parent());
   DCHECK_EQ(this, other->parent());
-  size_t child_i =
+
+  const size_t child_i =
       std::find(children_.begin(), children_.end(), child) - children_.begin();
-  size_t other_i =
+  const size_t other_i =
       std::find(children_.begin(), children_.end(), other) - children_.begin();
-  if (child_i > other_i)
-    return;  // Already in front of |other|.
+  if (child_i == other_i + 1)
+    return;
 
-  // Reorder children.
+  const size_t dest_i = child_i < other_i ? other_i : other_i + 1;
   children_.erase(children_.begin() + child_i);
-  children_.insert(children_.begin() + other_i, child);
+  children_.insert(children_.begin() + dest_i, child);
 
   SetNeedsToRecomputeHole();
 
 #if defined(USE_WEBKIT_COMPOSITOR)
   child->web_layer_.removeFromParent();
-  web_layer_.insertChild(child->web_layer_, other_i);
+  web_layer_.insertChild(child->web_layer_, dest_i);
 #endif
 }
 
 bool Layer::Contains(const Layer* other) const {
   for (const Layer* parent = other; parent; parent = parent->parent()) {
     if (parent == this)
       return true;
   }
   return false;
 }
@@ skipping 569 matching lines @@
         0,
         static_cast<float>(size.width())/texture_cc->size().width(),
         static_cast<float>(size.height())/texture_cc->size().height());
     texture_layer.setUVRect(rect);
     web_layer_.setBounds(size);
   }
 }
 #endif
 
 }  // namespace ui