MacViews: Fix sending mouse exit event and releasing capture on D&D.

ui/views/cocoa/drag_drop_client_mac.mm

 // Copyright 2016 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.
 
 #import "ui/views/cocoa/drag_drop_client_mac.h"
 
 #include "base/mac/mac_util.h"
 #include "base/run_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ui/base/dragdrop/os_exchange_data_provider_mac.h"
@@ skipping 61 matching lines @@
     View* view,
     const ui::OSExchangeData& data,
     int operation,
     ui::DragDropTypes::DragEventSource source) {
   data_source_.reset([[CocoaDragDropDataProvider alloc] initWithData:data]);
   operation_ = operation;
 
   const ui::OSExchangeDataProviderMac& provider =
       static_cast<const ui::OSExchangeDataProviderMac&>(data.provider());
 
+  // Release capture before beginning the dragging session. Capture may have
+  // been acquired on the mouseDown, but capture is not required during the
+  // dragging session and the mouseUp that would release it will be suppressed.
+  bridge_->ReleaseCapture();
+
   // Synthesize an event for dragging, since we can't be sure that
   // [NSApp currentEvent] will return a valid dragging event.
   NSWindow* window = bridge_->ns_window();
   NSPoint position = [window mouseLocationOutsideOfEventStream];
   NSTimeInterval event_time = [[NSApp currentEvent] timestamp];
   NSEvent* event = [NSEvent mouseEventWithType:NSLeftMouseDragged
                                       location:position
                                  modifierFlags:NSLeftMouseDraggedMask
                                      timestamp:event_time
                                   windowNumber:[window windowNumber]
@@ skipping 67 matching lines @@
     quit_closure_.Run();
     quit_closure_.Reset();
   }
 }
 
 gfx::Point DragDropClientMac::LocationInView(NSPoint point) const {
   return gfx::Point(point.x, NSHeight([bridge_->ns_window() frame]) - point.y);
 }
 
 }  // namespace views