Mac: Fix for janky tab dragging/reordering.

-[TabView drawRect:] was called repeatedly to unnecessarily update the glow
that is not changing or should not have changed.

1. Selected tabs don't have glow, so don't redraw on mouseMoved.

2. When dragging an unselected tab, the mouse point relative to the tab view
does not change, so no need to redraw the glow.

3. When a dragged unselected tab slides behind another tab, let the dragged tab
keep the glow instead of the tab in front of it (this is a behavior change).
I think this is the more correct behavior, and we never have to redraw tabs
while dragging.

BUG=452925

Review URL: https://codereview.chromium.org/882193003

Cr-Commit-Position: refs/heads/master@{#313734}

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

@@ -1867,6 +1867,12 @@ NSImage* Overlay(NSImage* ground, NSImage* overlay, CGFloat alpha) {
 }
 
 - (void)mouseMoved:(NSEvent*)event {
+  // We don't want the draggged tab to repeatedly redraw its glow unnecessarily.
+  // We also want the dragged tab to keep the glow even when it slides behind
+  // another tab.
+  if ([dragController_ draggedTab])
+    return;
+
   // Use hit test to figure out what view we are hovering over.
   NSView* targetView = [tabStripView_ hitTest:[event locationInWindow]];
 

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

@@ -59,6 +59,9 @@
   TabWindowController* targetController_;  // weak. Controller being targeted
 }
 
+// The tab being dragged, or nil if not dragging a tab.
+@property(readonly) TabController* draggedTab;
+
 // Designated initializer.
 - (id)initWithTabStripController:(TabStripController*)controller;
 

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

@@ -40,6 +40,8 @@ static BOOL PointIsInsideView(NSPoint screenPoint, NSView* view) {
 
 @implementation TabStripDragController
 
+@synthesize draggedTab = draggedTab_;
+
 - (id)initWithTabStripController:(TabStripController*)controller {
   if ((self = [super init])) {
     tabStrip_ = controller;

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

@@ -136,9 +136,10 @@ const CGFloat kRapidCloseDist = 2.5;
 }
 
 - (void)mouseMoved:(NSEvent*)theEvent {
-  hoverPoint_ = [self convertPoint:[theEvent locationInWindow]
-                          fromView:nil];
-  [self setNeedsDisplay:YES];
+  if (state_ == NSOffState) {
+    hoverPoint_ = [self convertPoint:[theEvent locationInWindow] fromView:nil];
+    [self setNeedsDisplay:YES];
+  }
 }
 
 - (void)mouseExited:(NSEvent*)theEvent {