Record a success stat for each Windows touch drag drop.

This stat will be used by the team working on the WebUI
tab strip to determine how much of a real world problem
failure of touch drag of tabs in the tab strip is.

Failure is detected by ::DoDragDrop blocking for more than one second
and only calling QueryContinueDrag once.

Bug: 1126230
Change-Id: I75b9d3a95912b8ef2ec049fcd32ed4700e4ca51d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437485
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812685}

tools/metrics/histograms/histograms_xml/windows/histograms.xml

@@ -292,6 +292,22 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Windows.TouchDrag.Success" units="BooleanSuccess"
+    expires_after="2021-03-01">
+  <owner>davidbienvenu@chromium.org</owner>
+  <owner>dfried@chromium.org</owner>
+  <summary>
+    Recorded each time the user starts a Windows touch drag drop of web
+    contents. This is currently only used by the WebUI tab strip, where touch
+    drag drop is enabled, to count the number of touch drags attempted.
+    ::DoDragDrop occasionally blocks waiting for a right mouse button down
+    followed by a move, which is detected by ::DoDragDrop not calling
+    QueryContinueDrag for more than a second. This will be recorded as false.
+    This stat will be used to determine how much of a real world problem this
+    is.
+  </summary>
+</histogram>
+
 </histograms>
 
 </histogram-configuration>

ui/base/dragdrop/drag_source_win.cc

@@ -16,6 +16,7 @@ DragSourceWin::DragSourceWin() : cancel_drag_(false), data_(nullptr) {
 }
 
 HRESULT DragSourceWin::QueryContinueDrag(BOOL escape_pressed, DWORD key_state) {
+  num_query_continues_++;
   if (cancel_drag_)
     return DRAGDROP_S_CANCEL;
 

ui/base/dragdrop/drag_source_win.h

@@ -42,6 +42,10 @@ class DragSourceWin
     cancel_drag_ = true;
   }
 
+  // This is used to tell if the drag drop actually started, for generating
+  // a BooleanSuccess histogram.
+  int num_query_continues() const { return num_query_continues_; }
+
   // IDropSource implementation:
   HRESULT __stdcall QueryContinueDrag(BOOL escape_pressed,
                                       DWORD key_state) override;
@@ -63,6 +67,12 @@ class DragSourceWin
 
   const OSExchangeData* data_;
 
+  // The number of times for this drag that Windows asked if the drag should
+  // continue. This is used in DesktopDragDropClientWin::StartDragAndDrop to
+  // detect if touch drag drop started successfully. See comment there for much
+  // more info.
+  int num_query_continues_ = 0;
+
   DISALLOW_COPY_AND_ASSIGN(DragSourceWin);
 };
 

ui/views/widget/desktop_aura/desktop_drag_drop_client_win.cc

@@ -6,6 +6,7 @@
 
 #include <memory>
 
+#include "base/metrics/histogram_macros.h"
 #include "base/threading/hang_watcher.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/base/dragdrop/drag_source_win.h"
@@ -72,12 +73,32 @@ int DesktopDragDropClientWin::StartDragAndDrop(
   // Disable hang watching until the end of the function since the user can take
   // unbounded time to complete the drag. (http://crbug.com/806174)
   base::HangWatchScopeDisabled disabler;
+  base::TimeTicks start_time = base::TimeTicks::Now();
 
   HRESULT result = ::DoDragDrop(
       ui::OSExchangeDataProviderWin::GetIDataObject(*data.get()),
       drag_source_.Get(),
       ui::DragDropTypes::DragOperationToDropEffect(operation), &effect);
   if (alive && source == ui::mojom::DragEventSource::kTouch) {
+    // In a normal drag drop, ::DoDragDrop calls QueryContinueDrag every time
+    // it gets a mouse or keyboard event. The windows doc
+    // https://docs.microsoft.com/en-us/windows/win32/api/oleidl/nf-oleidl-idropsource-querycontinuedrag
+    // says "every time it detects a change in keyboard or mouse button state"
+    // but empirically, on a Yoga laptop with a touch screen running Windows 10,
+    // it's called when it gets a mouse move event as well. (::DoDragDrop
+    // doesn't support touch, so Chrome synthesizes mouse events from touch
+    // events during drag drop.)
+    // In the touch failure case, when ::DoDragDrop blocks waiting for a right
+    // mouse button down event to start the drag, it only calls
+    // QueryContinueDrag once, when it gets an event that terminates the blocked
+    // drag drop, e.g., a swipe gesture from outside the Chrome window. So, we
+    // detect the failure case when a drag drop lasts more than one second, and
+    // QueryContinueDrag was not called more than once.
+    // See crbug.com/1126230.
+    UMA_HISTOGRAM_BOOLEAN("Windows.TouchDrag.Success",
+                          drag_source_->num_query_continues() > 1 ||
+                              (base::TimeTicks::Now() - start_time <
+                               base::TimeDelta::FromSeconds(1)));
     desktop_host_->SetInTouchDrag(false);
   }
   drag_source_copy->set_data(nullptr);