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

ui/events/gestures/gesture_recognizer_impl.cc

Index: ui/events/gestures/gesture_recognizer_impl.cc
diff --git a/ui/events/gestures/gesture_recognizer_impl.cc b/ui/events/gestures/gesture_recognizer_impl.cc
index d2316d4d0ca9555d489906dda27a9027e4b067cb..c27af4aaafdce5247c72a2ed3b375c43fbf4ddb9 100644
--- a/ui/events/gestures/gesture_recognizer_impl.cc
+++ b/ui/events/gestures/gesture_recognizer_impl.cc
@@ -68,9 +68,29 @@ GestureProviderAura* CreateGestureProvider(GestureProviderAuraClient* client) {
 ////////////////////////////////////////////////////////////////////////////////
 // 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_gd_enabled_switch =
+      command_line.HasSwitch(switches::kUnifiedGestureDetector) ?
+      command_line.GetSwitchValueASCII(switches::kUnifiedGestureDetector) :
+      switches::kUnifiedGestureDetectorAuto;
+
+  const bool kUseUnifiedGestureDetectorByDefault = false;
+  if (unified_gd_enabled_switch.empty() ||
+      unified_gd_enabled_switch == switches::kUnifiedGestureDetectorEnabled) {
+    use_unified_gesture_detector_ = true;
+  } else if (unified_gd_enabled_switch ==
+                 switches::kUnifiedGestureDetectorDisabled) {
+    use_unified_gesture_detector_ = false;
+  } else if (unified_gd_enabled_switch ==
+             switches::kUnifiedGestureDetectorAuto) {
+    use_unified_gesture_detector_ = kUseUnifiedGestureDetectorByDefault;
+  } else {
+    LOG(ERROR) << "Invalid --unified-gesture-detector option: "
+               << unified_gd_enabled_switch;
+    use_unified_gesture_detector_ = false;
+  }
 }
 
 GestureRecognizerImpl::~GestureRecognizerImpl() {