Allow synthetic Tap gestures without a preceding TapDown

While TapDown gestures are a typical part of the touch-gesture pipeline,
they are not required and probably even undesirable in the case of
synthetic Tap gestures (e.g., with tap disambiguation). Allow such
synthetic taps through the gesture stream validator.

BUG=414372

Review URL: https://codereview.chromium.org/572853005

Cr-Commit-Position: refs/heads/master@{#295141}

content/common/input/gesture_event_stream_validator.cc

@@ -62,13 +62,19 @@ bool GestureEventStreamValidator::Validate(const blink::WebGestureEvent& event,
         error_msg->append("Missing tap end event\n");
       waiting_for_tap_end_ = true;
       break;
-    case WebInputEvent::GestureTap:
+    case WebInputEvent::GestureTapUnconfirmed:
+      if (!waiting_for_tap_end_)
+        error_msg->append("Missing TapDown event before TapUnconfirmed\n");
+      break;
     case WebInputEvent::GestureTapCancel:
       if (!waiting_for_tap_end_)
-        error_msg->append("Missing GestureTapDown event\n");
+        error_msg->append("Missing TapDown event before TapCancel\n");
       waiting_for_tap_end_ = false;
       break;
+    case WebInputEvent::GestureTap:
     case WebInputEvent::GestureDoubleTap:
+      // Both Tap and DoubleTap gestures may be synthetically inserted, and do
+      // not require a preceding TapDown.
       waiting_for_tap_end_ = false;
       break;
     default:

content/common/input/gesture_event_stream_validator_unittest.cc

@@ -165,7 +165,7 @@ TEST(GestureEventStreamValidator, ValidTap) {
   EXPECT_TRUE(validator.Validate(event, &error_msg));
   EXPECT_TRUE(error_msg.empty());
 
-  event = Build(WebInputEvent::GestureTap);
+  event = Build(WebInputEvent::GestureTapCancel);
   EXPECT_TRUE(validator.Validate(event, &error_msg));
   EXPECT_TRUE(error_msg.empty());
 
@@ -173,11 +173,20 @@ TEST(GestureEventStreamValidator, ValidTap) {
   EXPECT_TRUE(validator.Validate(event, &error_msg));
   EXPECT_TRUE(error_msg.empty());
 
+  event = Build(WebInputEvent::GestureTapUnconfirmed);
+  EXPECT_TRUE(validator.Validate(event, &error_msg));
+  EXPECT_TRUE(error_msg.empty());
+
   event = Build(WebInputEvent::GestureTapCancel);
   EXPECT_TRUE(validator.Validate(event, &error_msg));
   EXPECT_TRUE(error_msg.empty());
 
-  // DoubleTap doesn't require a TapDown (unlike Tap and TapCancel).
+  // Tap and DoubleTap do not require a TapDown (unlike TapUnconfirmed and
+  // TapCancel).
+  event = Build(WebInputEvent::GestureTap);
+  EXPECT_TRUE(validator.Validate(event, &error_msg));
+  EXPECT_TRUE(error_msg.empty());
+
   event = Build(WebInputEvent::GestureDoubleTap);
   EXPECT_TRUE(validator.Validate(event, &error_msg));
   EXPECT_TRUE(error_msg.empty());
@@ -189,7 +198,7 @@ TEST(GestureEventStreamValidator, InvalidTap) {
   WebGestureEvent event;
 
   // No preceding TapDown.
-  event = Build(WebInputEvent::GestureTap);
+  event = Build(WebInputEvent::GestureTapUnconfirmed);
   EXPECT_FALSE(validator.Validate(event, &error_msg));
   EXPECT_FALSE(error_msg.empty());
 
@@ -209,6 +218,19 @@ TEST(GestureEventStreamValidator, InvalidTap) {
   event = Build(WebInputEvent::GestureTapCancel);
   EXPECT_FALSE(validator.Validate(event, &error_msg));
   EXPECT_FALSE(error_msg.empty());
+
+  // TapDown already terminated.
+  event = Build(WebInputEvent::GestureTapDown);
+  EXPECT_TRUE(validator.Validate(event, &error_msg));
+  EXPECT_TRUE(error_msg.empty());
+
+  event = Build(WebInputEvent::GestureTap);
+  EXPECT_TRUE(validator.Validate(event, &error_msg));
+  EXPECT_TRUE(error_msg.empty());
+
+  event = Build(WebInputEvent::GestureTapCancel);
+  EXPECT_FALSE(validator.Validate(event, &error_msg));
+  EXPECT_FALSE(error_msg.empty());
 }
 
 }  // namespace content