Add float version of gfx::Range

ui/gfx/range/range_mac.mm

 // 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/range/range.h"
 
 #include <limits>
 
 #include "base/logging.h"
 
 namespace gfx {
 
-Range::Range(const NSRange& range) {
+Range::Range(const NSRange& range)
+    : TRangeBase(0, 0) {
   *this = range;
 }
 
 Range& Range::operator=(const NSRange& range) {
   if (range.location == NSNotFound) {
     DCHECK_EQ(0U, range.length);
     *this = InvalidRange();
   } else {
     set_start(range.location);
     // Don't overflow |end_|.
     DCHECK_LE(range.length, std::numeric_limits<size_t>::max() - start());
     set_end(start() + range.length);
   }
   return *this;
 }
 
 NSRange Range::ToNSRange() const {
   if (!IsValid())
     return NSMakeRange(NSNotFound, 0);
   return NSMakeRange(GetMin(), length());
 }
 
 }  // namespace gfx