ui: Remove gfx::Size::ClampToNonNegative, prevent negative sizes always.

ui/ui.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     'ui_resources.gypi',
@@ skipping 478 matching lines @@
         'gfx/screen_win.h',
         'gfx/scrollbar_size.cc',
         'gfx/scrollbar_size.h',
         'gfx/selection_model.cc',
         'gfx/selection_model.h',
         'gfx/shadow_value.cc',
         'gfx/shadow_value.h',
         'gfx/size.cc',
         'gfx/size.h',
         'gfx/size_base.h',
+        'gfx/size_base_impl.h',
         'gfx/size_conversions.cc',
         'gfx/size_conversions.h',
         'gfx/size_f.cc',
         'gfx/size_f.h',
         'gfx/skbitmap_operations.cc',
         'gfx/skbitmap_operations.h',
         'gfx/skia_util.cc',
         'gfx/skia_util.h',
         'gfx/skia_utils_gtk.cc',
         'gfx/skia_utils_gtk.h',
@@ skipping 381 matching lines @@
            },
            'dependencies': [
              '../base/base.gyp:base_java',
            ],
            'includes': [ '../build/java.gypi' ],
          },
        ],
     }],
   ],
 }