Add a dead zone when dragging tabs horizontally on Mac

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

Index: chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm
diff --git a/chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm b/chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm
index 3d168310cbb5820ab90d3ccf9d4b9e060d6e76ba..074476a276614c9312140774a33caf325561f25b 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm
@@ -17,6 +17,7 @@
 #include "ui/base/cocoa/cocoa_base_utils.h"
 #include "ui/gfx/mac/scoped_cocoa_disable_screen_updates.h"
 
+const CGFloat kHorizontalTearDistance = 10.0; // Using the same value as Views.
 const CGFloat kTearDistance = 36.0;
 const NSTimeInterval kTearDuration = 0.333;
 
@@ -171,9 +172,17 @@ static BOOL PointIsInsideView(NSPoint screenPoint, NSView* view) {
   if (draggingWithinTabStrip_) {
     NSPoint thisPoint = [NSEvent mouseLocation];
     CGFloat offset = thisPoint.x - dragOrigin_.x;
-    [sourceController_ insertPlaceholderForTab:[draggedTab_ tabView]
-                                         frame:NSOffsetRect(sourceTabFrame_,
-                                                            offset, 0)];
+    // Only begin dragging the tab horizontally if it's torn out of its dead
+    // zone.
+    if (!outOfTabHorizontalDeadZone_ &&
+        fabs(offset) > kHorizontalTearDistance) {
+      outOfTabHorizontalDeadZone_ = YES;
+    }
+    if (outOfTabHorizontalDeadZone_) {

[erikchen, 2016/11/30 21:07:34]

I patched this in and tried tab dragging. It seemed to work fine, but I also saw
a large number of:

"""
tab_window_controller.mm(352)] Not implemented reached in -[TabWindowController
menubarOffset]
"""

It's not clear to me how you're actually preventing tab dragging by inserting a
placeholder on line 182. I imagine that you want an early return? Can you
explain how you're trying to prevent tab dragging? 

[njagsarran, 2016/12/02 16:43:12]

I'm seeing that error, too. I undid my changed and rebuilt, but I'm still seeing
that error. Do you also still see it without my patch, or am I missing
something?

I think the placeholder is the tab under the mouse when moving it within the
strip, so now it can't be created unless we drag beyond the dead zone. I don't
think we want an early return because we still want to check for vertical
dragging below.

[erikchen, 2016/12/07 17:53:20]

You're right. Tried again and I can reproduce the error withyour your CL. 

It looks like placeholderTab_ is used to determine "isDragSessionActive", which
is why setting it is required to start dragging.

+      [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.
@@ -403,6 +412,7 @@ static BOOL PointIsInsideView(NSPoint screenPoint, NSView* view) {
 - (void)endDrag:(NSEvent*)event {
   // Cancel any delayed -continueDrag: requests that may still be pending.
   [NSObject cancelPreviousPerformRequestsWithTarget:self];
+  outOfTabHorizontalDeadZone_ = NO;
 
   // Special-case this to keep the logic below simpler.
   if (moveWindowOnDrag_) {