Expose native, desktop and mobile gesture detection defaults

ui/events/gesture_detection/scale_gesture_detector.cc

 // Copyright 2014 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/events/gesture_detection/scale_gesture_detector.h"
 
 #include <limits.h>
 #include <cmath>
 
 #include "base/float_util.h"
@@ skipping 12 matching lines @@
 // region and DPI scale are reasonably proportioned).
 const float kSlopEpsilon = .05f;
 
 const int kTouchStabilizeTimeMs = 128;
 
 const float kScaleFactor = .5f;
 
 }  // namespace
 
 // Note: These constants were taken directly from the default (unscaled)
-// versions found in Android's ViewConfiguration.
+// versions found in Android's ViewConfiguration. Do not change these default
+// values without explicitly consulting an OWNER.
 ScaleGestureDetector::Config::Config()
     : span_slop(16),
       min_scaling_touch_major(48),
       min_scaling_span(200),
       min_pinch_update_span_delta(0) {
 }
 
 ScaleGestureDetector::Config::~Config() {}
 
 ScaleGestureDetector::ScaleGestureDetector(const Config& config,
@@ skipping 301 matching lines @@
   touch_history_last_accepted_time_ = base::TimeTicks();
 }
 
 void ScaleGestureDetector::ResetScaleWithSpan(float span) {
   in_progress_ = false;
   initial_span_ = span;
   double_tap_mode_ = DOUBLE_TAP_MODE_NONE;
 }
 
 }  // namespace ui