Fix tab strip drag-to-open bugs

Fixes the following:
- Fractional part of drag updates was thrown away, causing the current
  height to lag behind the touch position. The error compounded the
  longer the drag was in progress.
- Tab strip got stuck when dragged slowly to the fully open or closed
  position. Animations don't get run when they're at their target value,
  but I assumed otherwise.
- Incorrect assumptions about ordering of ET_GESTURE_SCROLL_END,
  ET_GESTURE_SWIPE, and ET_GESTURE_END resulted in occasional DCHECKs.
  Changed to be more permissive.

Bug: 1043374
Change-Id: Iedab85a33bf6c89b51f1a88e73864ba32e885781
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076783Reviewed-by: Taylor Bergquist <tbergquist@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745638}

chrome/browser/ui/views/frame/webui_tab_strip_container_view.cc

@@ -170,24 +170,28 @@ class WebUITabStripContainerView::DragToOpenHandler : public ui::EventHandler {
     switch (event->type()) {
       case ui::ET_GESTURE_SCROLL_BEGIN:
         drag_in_progress_ = true;
+        container_->UpdateHeightForDragToOpen(event->details().scroll_y_hint());
         event->SetHandled();
         break;
       case ui::ET_GESTURE_SCROLL_UPDATE:
-        DCHECK(drag_in_progress_);
+        if (drag_in_progress_) {
           container_->UpdateHeightForDragToOpen(event->details().scroll_y());
           event->SetHandled();
+        }
         break;
       case ui::ET_GESTURE_SCROLL_END:
-        DCHECK(drag_in_progress_);
+        if (drag_in_progress_) {
           container_->EndDragToOpen(false);
           event->SetHandled();
           drag_in_progress_ = false;
+        }
         break;
       case ui::ET_GESTURE_SWIPE:
         // If a touch is released at high velocity, the scroll gesture
-        // is "converted" to a swipe gesture. Note that a
-        // ET_GESTURE_SCROLL_END event will not be sent. ET_GESTURE_END
-        // is still sent after, however.
+        // is "converted" to a swipe gesture. ET_GESTURE_END is still
+        // sent after. From logging, it seems like ET_GESTURE_SCROLL_END
+        // is sometimes also sent after this. It will be ignored here
+        // since |drag_in_progress_| is set to false.
         DCHECK(drag_in_progress_);
         container_->EndDragToOpen(event->details().swipe_down());
         event->SetHandled();
@@ -391,7 +395,7 @@ void WebUITabStripContainerView::CloseContainer() {
   iph_tracker_->NotifyEvent(feature_engagement::events::kWebUITabStripClosed);
 }
 
-void WebUITabStripContainerView::UpdateHeightForDragToOpen(int height_delta) {
+void WebUITabStripContainerView::UpdateHeightForDragToOpen(float height_delta) {
   if (!current_drag_height_) {
     // If we are visible and aren't already dragging, ignore; either we are
     // animating open, or the touch would've triggered autoclose.
@@ -403,8 +407,9 @@ void WebUITabStripContainerView::UpdateHeightForDragToOpen(int height_delta) {
     animation_.Reset();
   }
 
-  current_drag_height_ = base::ClampToRange(
-      *current_drag_height_ + height_delta, 0, desired_height_);
+  current_drag_height_ =
+      base::ClampToRange(*current_drag_height_ + height_delta, 0.0f,
+                         static_cast<float>(desired_height_));
   PreferredSizeChanged();
 }
 
@@ -433,8 +438,12 @@ void WebUITabStripContainerView::SetContainerTargetVisibility(
     bool target_visible) {
   if (target_visible) {
     SetVisible(true);
+    PreferredSizeChanged();
+    if (animation_.GetCurrentValue() < 1.0) {
       animation_.SetSlideDuration(base::TimeDelta::FromMilliseconds(250));
       animation_.Show();
+    }
+
     web_view_->SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
     time_at_open_ = base::TimeTicks::Now();
 
@@ -454,8 +463,14 @@ void WebUITabStripContainerView::SetContainerTargetVisibility(
       time_at_open_ = base::nullopt;
     }
 
+    if (animation_.GetCurrentValue() > 0.0) {
       animation_.SetSlideDuration(base::TimeDelta::FromMilliseconds(200));
       animation_.Hide();
+    } else {
+      PreferredSizeChanged();
+      SetVisible(false);
+    }
+
     web_view_->SetFocusBehavior(FocusBehavior::NEVER);
 
     // Tapping in the WebUI tab strip gives keyboard focus to the
@@ -564,7 +579,7 @@ int WebUITabStripContainerView::GetHeightForWidth(int w) const {
                                              desired_height_);
   }
   if (current_drag_height_)
-    return *current_drag_height_;
+    return std::round(*current_drag_height_);
 
   return GetVisible() ? desired_height_ : 0;
 }

chrome/browser/ui/views/frame/webui_tab_strip_container_view.h

@@ -89,7 +89,7 @@ class WebUITabStripContainerView : public TabStripUIEmbedder,
   class DragToOpenHandler;
 
   // Called as we are dragged open.
-  void UpdateHeightForDragToOpen(int height_delta);
+  void UpdateHeightForDragToOpen(float height_delta);
 
   // Called when drag-to-open finishes. If |fling_to_open| is true, the
   // user released their touch with a high enough velocity that we
@@ -145,7 +145,7 @@ class WebUITabStripContainerView : public TabStripUIEmbedder,
   views::View* tab_counter_ = nullptr;
 
   int desired_height_ = 0;
-  base::Optional<int> current_drag_height_;
+  base::Optional<float> current_drag_height_;
 
   // When opened, if currently open. Used to calculate metric for how
   // long the tab strip is kept open.