Use multi-value switch to enable/disable the unified gesture detector.

ui/events/gestures/gesture_recognizer_impl.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 "ui/events/gestures/gesture_recognizer_impl.h"
 
 #include <limits>
 
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 50 matching lines @@
 
 GestureProviderAura* CreateGestureProvider(GestureProviderAuraClient* client) {
   return new GestureProviderAura(client);
 }
 
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
 // GestureRecognizerImpl, public:
 
-GestureRecognizerImpl::GestureRecognizerImpl()
-    : use_unified_gesture_detector_(CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kUseUnifiedGestureDetector)) {
+GestureRecognizerImpl::GestureRecognizerImpl() {
+  // Default to not using the unified gesture detector.
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  const std::string unified_gr_enabled_switch =
+      command_line.HasSwitch(switches::kUnifiedGestureDetector) ?
+      command_line.GetSwitchValueASCII(switches::kUnifiedGestureDetector) :
+      switches::kUnifiedGestureDetectorAuto;
+
+  if (unified_gr_enabled_switch.empty() ||
+      unified_gr_enabled_switch == switches::kUnifiedGestureDetectorEnabled) {
+    use_unified_gesture_detector_ = true;
+  } else if (unified_gr_enabled_switch ==
+                 switches::kUnifiedGestureDetectorAuto ||
+             unified_gr_enabled_switch ==
+                 switches::kUnifiedGestureDetectorDisabled) {
+    use_unified_gesture_detector_ = false;

[sadrul, 2014/05/22 18:45:25]

Can you do:

  const bool kUseUnifiedDefault = false;
  if (switch empty or enabled) use_unified = true;
  else if (switch disabled) use_unified = false;
  else use_unified = kUseUnifiedDefault;

That way, switching the default would involve changing just the const bool's
value.
  

[tdresser, 2014/05/22 19:13:04]

Done.

+  } else {
+    LOG(ERROR) << "Invalid --unified-gesture-detector option: "
+               << unified_gr_enabled_switch;
+    use_unified_gesture_detector_ = false;
+  }
 }
 
 GestureRecognizerImpl::~GestureRecognizerImpl() {
   STLDeleteValues(&consumer_sequence_);
   STLDeleteValues(&consumer_gesture_provider_);
 }
 
 // Checks if this finger is already down, if so, returns the current target.
 // Otherwise, returns NULL.
 GestureConsumer* GestureRecognizerImpl::GetTouchLockedTarget(
@@ skipping 309 matching lines @@
   std::vector<GestureEventHelper*>::iterator it;
   for (it = helpers.begin(); it != helpers.end(); ++it)
     gesture_recognizer->AddGestureEventHelper(*it);
 
   helpers.clear();
   g_gesture_recognizer_instance =
       static_cast<GestureRecognizerImpl*>(gesture_recognizer);
 }
 
 }  // namespace ui