Refactor intra-strip panel drags by introducing PanelDragController.

chrome/browser/ui/panels/panel_titlebar_view_cocoa.mm

Index: chrome/browser/ui/panels/panel_titlebar_view_cocoa.mm
diff --git a/chrome/browser/ui/panels/panel_titlebar_view_cocoa.mm b/chrome/browser/ui/panels/panel_titlebar_view_cocoa.mm
index c3ff9d4fba400b489f6a9ec2c062f300129bfc30..0c93d636ec9cbbcd49a79ab8cc31fc494f00ebde 100644
--- a/chrome/browser/ui/panels/panel_titlebar_view_cocoa.mm
+++ b/chrome/browser/ui/panels/panel_titlebar_view_cocoa.mm
@@ -436,7 +436,8 @@ static NSEvent* MakeMouseEvent(NSEventType type,
             return;  // Don't start real drag yet.
           [self startDrag];
         }
-        [self dragWithDeltaX:[event deltaX]];
+        [self dragWithDeltaX:[event deltaX]
+                      deltaY:[event deltaY]];
         break;
 
       case NSKeyUp:
@@ -479,10 +480,12 @@ static NSEvent* MakeMouseEvent(NSEventType type,
   dragState_ = PANEL_DRAG_SUPPRESSED;
 }
 
-- (void)dragWithDeltaX:(int)deltaX {
+- (void)dragWithDeltaX:(int)deltaX
+                deltaY:(int)deltaY {
   if (dragState_ != PANEL_DRAG_IN_PROGRESS)
     return;
-  [controller_ dragWithDeltaX:deltaX];
+  [controller_ dragWithDeltaX:deltaX
+                       deltaY:deltaY];
 }
 
 - (void)drawAttention {
@@ -580,7 +583,8 @@ static NSEvent* MakeMouseEvent(NSEventType type,
                     deltaY:(double)delta_y {
   if (dragState_ == PANEL_DRAG_CAN_START)
     [self startDrag];
-  [self dragWithDeltaX:delta_x];
+  [self dragWithDeltaX:delta_x
+                deltaY:delta_y];
 }
 
 - (void)cancelDragTitlebar {