[Mac] Implement highlight-on-hover for the Wrench menu buttons.

chrome/browser/cocoa/menu_tracked_button.mm

Index: chrome/browser/cocoa/menu_tracked_button.mm
diff --git a/chrome/browser/cocoa/menu_tracked_button.mm b/chrome/browser/cocoa/menu_tracked_button.mm
index 654e850243b4d0ac0e91cde08518e6eb66a84fa8..eddb733c1091c8bcd88bc782c4e691b002c82fdd 100644
--- a/chrome/browser/cocoa/menu_tracked_button.mm
+++ b/chrome/browser/cocoa/menu_tracked_button.mm
@@ -4,29 +4,111 @@
 
 #import "chrome/browser/cocoa/menu_tracked_button.h"
 
+#include <cmath>
+
+@interface MenuTrackedButton (Private)
+- (void)doHighlight:(BOOL)highlight;
+- (void)checkMouseInRect;
+- (NSRect)insetBounds;
+- (BOOL)shouldHighlightOnHover;
+@end
+
 @implementation MenuTrackedButton
 
+- (void)updateTrackingAreas {
+  [super updateTrackingAreas];
+  [self removeTrackingRect:trackingTag_];
+  trackingTag_ = [self addTrackingRect:NSInsetRect([self bounds], 1, 1)
+                                 owner:self
+                              userData:NULL
+                          assumeInside:NO];
+}
+
+- (void)viewDidMoveToWindow {
+  [self updateTrackingAreas];
+  [self doHighlight:NO];
+}
+
 - (void)mouseEntered:(NSEvent*)theEvent {
-  didEnter_ = YES;
+  if (!tracking_) {
+    didEnter_ = YES;
+  }
+  [self doHighlight:YES];
   [super mouseEntered:theEvent];
 }
 
 - (void)mouseExited:(NSEvent*)theEvent {
   didEnter_ = NO;
   tracking_ = NO;
+  [self doHighlight:NO];
   [super mouseExited:theEvent];
 }
 
 - (void)mouseDragged:(NSEvent*)theEvent {
   tracking_ = !didEnter_;
+
+  NSPoint point = [self convertPoint:[theEvent locationInWindow] fromView:nil];
+  BOOL highlight = NSPointInRect(point, [self insetBounds]);
+  [self doHighlight:highlight];
+
+  // If tracking in non-sticky mode, poll the mouse cursor to see if it is still
+  // over the button and thus needs to be highlighted.  The delay is the largest
+  // value that works; smaller values make the selector fire too close to
+  // immediately/now for the mouse to have moved off the receiver.
+  if (tracking_ && [self shouldHighlightOnHover]) {
+    [self performSelector:@selector(checkMouseInRect)
+               withObject:nil
+               afterDelay:0.05
+                  inModes:[NSArray arrayWithObject:NSEventTrackingRunLoopMode]];
+  }
   [super mouseDragged:theEvent];
 }
 
 - (void)mouseUp:(NSEvent*)theEvent {
+  [self doHighlight:NO];
   if (!tracking_) {
     return [super mouseUp:theEvent];
   }
   [self performClick:self];
 }
 
+- (void)doHighlight:(BOOL)highlight {
+  if (![self shouldHighlightOnHover]) {
+    return;
+  }
+  [[self cell] setHighlighted:highlight];
+  [self setNeedsDisplay];
+}
+
+// Checks if the user's current mouse location is over this button.  If it is,
+// the user is merely hovering here.  If it is not, then disable the highlight.
+// If the menu is opened in non-sticky mode, the button does not receive enter/
+// exit mouse events and thus polling is necessary.
+- (void)checkMouseInRect {
+  NSPoint point = [NSEvent mouseLocation];
+  point = [[self window] convertScreenToBase:point];
+  point = [self convertPoint:point fromView:nil];
+  if (!NSPointInRect(point, [self insetBounds])) {
+    [self doHighlight:NO];
+  }
+}
+
+// Returns the bounds of the receiver slightly inset to avoid highlighting both
+// buttons in a pair that overlap.
+- (NSRect)insetBounds {
+  return NSInsetRect([self bounds], 2, 1);
+}
+
+- (BOOL)shouldHighlightOnHover {
+  // Apple does not define NSAppKitVersionNumber10_5 when using the 10.5 SDK.
+  // The Internets have come up with this solution.
+  #ifndef NSAppKitVersionNumber10_5
+  #define NSAppKitVersionNumber10_5 949
+  #endif
+
+  // There's a cell drawing bug in 10.5 that was fixed on 10.6.  Hover states
+  // look terrible due to this, so disable highlighting on 10.5.
+  return std::floor(NSAppKitVersionNumber) > NSAppKitVersionNumber10_5;
+}
+
 @end