[MacViews] Enable dragging a window by its caption/draggable areas.

ui/views/cocoa/bridged_native_widget.mm

Index: ui/views/cocoa/bridged_native_widget.mm
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index 107896f931f200368571f936db5dd58cc4eebeb7..7025517f72ddcaa10cdd2cacc54434678af8a6f5 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -10,6 +10,7 @@
 #include "base/mac/mac_util.h"
 #import "base/mac/sdk_forward_declarations.h"
 #include "base/thread_task_runner_handle.h"
+#include "ui/base/hit_test.h"
 #include "ui/base/ime/input_method.h"
 #include "ui/base/ime/input_method_factory.h"
 #include "ui/base/ui_base_switches_util.h"
@@ -19,6 +20,7 @@
 #import "ui/gfx/mac/nswindow_frame_controls.h"
 #include "ui/gfx/screen.h"
 #import "ui/views/cocoa/cocoa_mouse_capture.h"
+#import "ui/views/cocoa/cocoa_non_client_drag.h"
 #import "ui/views/cocoa/bridged_content_view.h"
 #import "ui/views/cocoa/views_nswindow_delegate.h"
 #import "ui/views/cocoa/widget_owner_nswindow_adapter.h"
@@ -92,6 +94,7 @@ gfx::Size BridgedNativeWidget::GetWindowSizeForClientSize(
 
 BridgedNativeWidget::BridgedNativeWidget(NativeWidgetMac* parent)
     : native_widget_mac_(parent),
+      non_client_drag_(new CocoaNonClientDrag()),
       focus_manager_(nullptr),
       widget_type_(Widget::InitParams::TYPE_WINDOW),  // Updated in Init().
       parent_(nullptr),
@@ -522,6 +525,71 @@ void BridgedNativeWidget::OnWindowKeyStatusChangedTo(bool is_key) {
   }
 }
 
+bool BridgedNativeWidget::OnWindowWillReceiveLeftMouseDown(
+    NSPoint location_in_window) {
+  bool was_draggable = draggable_;
+  gfx::Point point(location_in_window.x,
+                   NSHeight([window_ frame]) - location_in_window.y);
+  draggable_ = native_widget_mac()->GetWidget()->GetNonClientComponent(point) ==
+               HTCAPTION;
+  LOG(INFO) << "OnWindowWillReceiveLeftMouseDown " << location_in_window.x
+            << ", " << location_in_window.y << " " << was_draggable << " "
+            << draggable_;
+////////////////////////////////////////////////////////////////////////////////
+// Behavior when using CGEventTap.
+/*
+  // If draggability has not changed, do nothing.
+  if (was_draggable == draggable_)
+    return false;
+
+  // Otherwise, either make the window draggable or non-draggable, then return
+  // true to repost the event.
+  NSView* content_view = [window_ contentView];
+  if (draggable_) {
+    NSView* mask_view = nil;
+    for (NSView* view in [content_view subviews]) {
+      if ([view isKindOfClass:[CocoaNonClientDragMaskView class]])
+        mask_view = view;
+    }
+    [mask_view removeFromSuperview];
+  } else {
+    base::scoped_nsobject<CocoaNonClientDragMaskView> mask_view(
+        [[CocoaNonClientDragMaskView alloc]
+            initWithFrame:[content_view bounds]]);
+    [content_view addSubview:mask_view];
+  }
+  return true;
+*/
+//
+////////////////////////////////////////////////////////////////////////////////
+// Behavior when using NSEvent local monitor.
+  NSView* content_view = [window_ contentView];
+  if (was_draggable) {
+    // This is a re-post, the movement has already completed, so we can make the
+    // window non-draggable again.
+    draggable_ = false;
+    base::scoped_nsobject<CocoaNonClientDragMaskView> mask_view(
+        [[CocoaNonClientDragMaskView alloc]
+            initWithFrame:[content_view bounds]]);
+    [content_view addSubview:mask_view];
+    return false;
+  }
+
+  if (draggable_) {
+    // Make the window draggable, then return true to repost the event.
+    NSView* mask_view = nil;
+    for (NSView* view in [content_view subviews]) {
+      if ([view isKindOfClass:[CocoaNonClientDragMaskView class]])
+        mask_view = view;
+    }
+    [mask_view removeFromSuperview];
+    return true;
+  }
+  return false;
+//
+////////////////////////////////////////////////////////////////////////////////
+}
+
 void BridgedNativeWidget::OnSizeConstraintsChanged() {
   NSWindow* window = ns_window();
   Widget* widget = native_widget_mac()->GetWidget();