linux_aura: Fix abs() warning found by new clang.

chrome/browser/ui/libgtk2ui/gtk2_ui.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/libgtk2ui/gtk2_ui.h"
 
 #include <set>
 
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
@@ skipping 228 matching lines @@
 
   color_utils::HSL background_tint;
   color_utils::SkColorToHSL(libgtk2ui::GdkColorToSkColor(background_color),
                             &background_tint);
 
   // If the accent color is gray, then our normal HSL tomfoolery will bring out
   // whatever color is oddly dominant (for example, in rgb space [125, 128,
   // 125] will tint green instead of gray). Slight differences (+/-10 (4%) to
   // all color components) should be interpreted as this color being gray and
   // we should switch into a special grayscale mode.
-  int rb_diff = abs(SkColorGetR(accent_color) - SkColorGetB(accent_color));
-  int rg_diff = abs(SkColorGetR(accent_color) - SkColorGetG(accent_color));
-  int bg_diff = abs(SkColorGetB(accent_color) - SkColorGetG(accent_color));
+  int rb_diff = abs(static_cast<int>(SkColorGetR(accent_color)) -
+                    static_cast<int>(SkColorGetB(accent_color)));
+  int rg_diff = abs(static_cast<int>(SkColorGetR(accent_color)) -
+                    static_cast<int>(SkColorGetG(accent_color)));
+  int bg_diff = abs(static_cast<int>(SkColorGetB(accent_color)) -
+                    static_cast<int>(SkColorGetG(accent_color)));
   if (rb_diff < 10 && rg_diff < 10 && bg_diff < 10) {
     // Our accent is white/gray/black. Only the luminance of the accent color
     // matters.
     tint->h = -1;
 
     // Use the saturation of the text.
     tint->s = text_tint.s;
 
     // Use the luminance of the accent color UNLESS there isn't enough
     // luminance contrast between the accent color and the base color.
@@ skipping 1121 matching lines @@
   ClearAllThemeData();
   LoadGtkValues();
   NativeThemeGtk2::instance()->NotifyObservers();
 }
 
 }  // namespace libgtk2ui
 
 views::LinuxUI* BuildGtk2UI() {
   return new libgtk2ui::Gtk2UI;
 }