Add a dead zone when dragging tabs horizontally on Mac

chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm

 // Copyright (c) 2012 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 "chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.h"
 
 #include <Carbon/Carbon.h>
 
 #include "base/mac/scoped_cftyperef.h"
 #import "base/mac/sdk_forward_declarations.h"
@@ skipping 153 matching lines @@
     return;
   }
 
   // First, go through the magnetic drag cycle. We break out of this if
   // "stretchiness" ever exceeds a set amount.
   tabWasDragged_ = YES;
 
   if (draggingWithinTabStrip_) {
     NSPoint thisPoint = [NSEvent mouseLocation];
     CGFloat offset = thisPoint.x - dragOrigin_.x;
+    // Only begin dragging the tab horizontally if it's torn out of its dead
+    // zone.
+    if (!outOfTabHorizontalDeadZone_ && fabs(offset) > kTearDistance) {

[Avi (use Gerrit), 2016/11/30 00:01:22]

Do we want kTearDistance? That's 36 pixels, and when I play on Views to see what
it does, the horizontal tear distance is a lot less.

What value does Views use here?

[erikchen, 2016/11/30 15:05:16]

Agreed that this should be significantly smaller. Given that the original bug
was about misclicks turning into horizontal drags, I'm thinking maybe 5, or even
3?

[njagsarran, 2016/11/30 17:44:49]

Looks like Views uses 10, what do you guys think of that? Still too much?

https://cs.chromium.org/chromium/src/chrome/browser/ui/views/tabs/tab_drag_co...

[njagsarran, 2016/11/30 20:26:32]

Done.

+      outOfTabHorizontalDeadZone_ = YES;
+    }
+    if (outOfTabHorizontalDeadZone_)

[Avi (use Gerrit), 2016/11/30 00:01:22]

You'd need to adjust the indentation here with a new if, and use {}.

[njagsarran, 2016/11/30 20:26:32]

Done.

     [sourceController_ insertPlaceholderForTab:[draggedTab_ tabView]
                                          frame:NSOffsetRect(sourceTabFrame_,
                                                             offset, 0)];
     // Check that we haven't pulled the tab too far to start a drag. This
     // can include either pulling it too far down, or off the side of the tab
     // strip that would cause it to no longer be fully visible.
     BOOL stillVisible =
         [sourceController_ isTabFullyVisible:[draggedTab_ tabView]];
     CGFloat tearForce = fabs(thisPoint.y - dragOrigin_.y);
     if ([sourceController_ tabTearingAllowed] &&
@@ skipping 238 matching lines @@
   // placeholder).
   [draggedController_ showNewTabButton:YES];
 
   if (draggingWithinTabStrip_) {
     if (tabWasDragged_) {
       // Move tab to new location.
       DCHECK([sourceController_ numberOfTabs]);
       TabWindowController* dropController = sourceController_;
       [dropController moveTabViews:@[ [dropController activeTabView] ]
                     fromController:nil];
+      outOfTabHorizontalDeadZone_ = NO;

[erikchen, 2016/11/30 15:05:16]

presumably we always want to reset this when the drag ends.

[njagsarran, 2016/11/30 20:26:32]

Done.

     }
   } else if (targetController_) {
     // Move between windows. If |targetController_| is nil, we're not dropping
     // into any existing window.
     [targetController_ moveTabViews:[draggedController_ tabViews]
                      fromController:draggedController_];
     // Force redraw to avoid flashes of old content before returning to event
     // loop.
     [[targetController_ window] display];
     [targetController_ showWindow:nil];
@@ skipping 113 matching lines @@
     [[targetController_ window] makeMainWindow];
   } else {
     [dragWindow_ setAlphaValue:0.5];
     [[draggedController_ overlayWindow] setHasShadow:NO];
     [[draggedController_ window] makeMainWindow];
   }
   chromeIsVisible_ = shouldBeVisible;
 }
 
 @end