compositor: Fix compositor_unittests build on Linux.

ui/gfx/compositor/layer_unittest.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 "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/canvas_skia.h"
 #include "ui/gfx/compositor/compositor_observer.h"
@@ skipping 16 matching lines @@
   gfx::Size paint_size() const { return paint_size_; }
   int color_index() const { return color_index_; }
 
   // Overridden from LayerDelegate:
   virtual void OnPaintLayer(gfx::Canvas* canvas) OVERRIDE {
     SkBitmap contents = canvas->AsCanvasSkia()->ExtractBitmap();
     paint_size_ = gfx::Size(contents.width(), contents.height());
     canvas->FillRectInt(colors_.at(color_index_), 0, 0,
                         contents.width(),
                         contents.height());
-    color_index_ = ++color_index_ % colors_.size();
+    color_index_ = (color_index_ + 1) % static_cast<int>(colors_.size());
   }
 
  private:
   Layer* owner_;
   std::vector<SkColor> colors_;
   int color_index_;
   gfx::Size paint_size_;
 
   DISALLOW_COPY_AND_ASSIGN(TestLayerDelegate);
 };
@@ skipping 247 matching lines @@
   RunPendingMessages();
 
   // |d2| should not have received a paint notification since it has no texture.
   EXPECT_FALSE(d2.painted());
   // |d3| should have received a paint notification.
   EXPECT_TRUE(d3.painted());
 }
 
 }  // namespace ui