[Not for review] Demo issue for discussion on https://codereview.chromium.org/2296903002/.

chrome/browser/ui/cocoa/fullscreen_toolbar_controller.mm

Index: chrome/browser/ui/cocoa/fullscreen_toolbar_controller.mm
diff --git a/chrome/browser/ui/cocoa/fullscreen_toolbar_controller.mm b/chrome/browser/ui/cocoa/fullscreen_toolbar_controller.mm
index e84f9ea822627483496c985b40cf39bfc6c69bfc..800640fcdc5a3c0583e44be1802d85e38bd89695 100644
--- a/chrome/browser/ui/cocoa/fullscreen_toolbar_controller.mm
+++ b/chrome/browser/ui/cocoa/fullscreen_toolbar_controller.mm
@@ -195,7 +195,6 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
     browserController_ = controller;
     systemFullscreenMode_ = base::mac::kFullScreenModeNormal;
     slidingStyle_ = style;
-    hiddenToolbarState_ = fullscreen_mac::TOOLBAR_HIDDEN;
   }
 
   // Install the Carbon event handler for the menubar show, hide and
@@ -298,7 +297,9 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
 
   [self cancelHideTimer];
   [self animateToolbarVisibility:NO];
-  shouldShowToolbarWithoutMenu_ = NO;
+
+  // The animation will tell us the appropriate progress.
+  // shouldShowToolbarWithoutMenu_ = NO;
 }
 
 - (void)cancelAnimationAndTimer {
@@ -317,7 +318,7 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
     return;
 
   // Reveal the toolbar for tabstrip changes if the toolbar is hidden.
-  if (hiddenToolbarState_ == fullscreen_mac::TOOLBAR_HIDDEN) {
+  if ([self toolbarFraction] == 0.0) {
     isRevealingToolbarForTabStripChanges_ = YES;
     [self showToolbarIfPossibleWithAnimation:YES];
   }
@@ -391,16 +392,42 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
     case fullscreen_mac::OMNIBOX_TABS_NONE:
       return kHideFraction;
     case fullscreen_mac::OMNIBOX_TABS_HIDDEN:
-      if (hiddenToolbarState_ == fullscreen_mac::TOOLBAR_SHOWN)
+      // If the menubar is showing, we always want to show the toolbar.
+      if (menubarState_ == fullscreen_mac::MENUBAR_SHOWN) {
+        return kShowFraction;
+      }
+
+      // If the menubar is animating in, and the toolbar was not already
+      // showing, then it should animate in at the same rate.
+      if (menubarState_ == fullscreen_mac::MENUBAR_TRANSITIONING && menubarAnimatingIn_ &&
+          !wasToolbarShowingWhenMenubarStartedAnimatingIn_) {
+        return menubarFraction_;
+      }
+
+      // If the menubar is animating in, and the toolbar is already showing,
+      // then continue to show it.
+      if (menubarState_ == fullscreen_mac::MENUBAR_TRANSITIONING &&
+          menubarAnimatingIn_) {
         return kShowFraction;
+      }
 
-      if (hiddenToolbarState_ == fullscreen_mac::TOOLBAR_HIDDEN)
-        return kHideFraction;
+      // If the menubar is animating out, we ignore!.
+      if (menubarState_ == fullscreen_mac::MENUBAR_TRANSITIONING &&
+          !menubarAnimatingIn_) {
+      }
 
+      // At this point, menubar is not showing. Is there a custom animation?
       if (currentAnimation_.get())
         return [currentAnimation_ toolbarFraction];
 
-      return shouldShowToolbarWithoutMenu_ ? kShowFraction : menubarFraction_;
+      // If mouse is in tracking rect, show toolbar:
+
+      // If there's a hide timer, show toolbar:
+
+      // Logic for show & hide tab strip on tab change...haven't thought through
+      // all the edge cases.
+
+      // Default: hide toolbar.
   }
 }
 
@@ -430,15 +457,9 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
 
 - (void)animationDidStop:(NSAnimation*)animation {
   CGFloat toolbarFraction = [self toolbarFraction];
-  if (IsCGFloatEqual(toolbarFraction, 1.0))
-    hiddenToolbarState_ = fullscreen_mac::TOOLBAR_SHOWN;
-  else if (IsCGFloatEqual(toolbarFraction, 0.0))
-    hiddenToolbarState_ = fullscreen_mac::TOOLBAR_HIDDEN;
-  else
-    hiddenToolbarState_ = fullscreen_mac::TOOLBAR_TRANSITIONING;
 
   if (isRevealingToolbarForTabStripChanges_) {
-    if (hiddenToolbarState_ != fullscreen_mac::TOOLBAR_HIDDEN) {
+    if (IsCGFloatEqual(toolbarFraction, 0.0)) {
       // Set the timer to hide the toolbar.
       [hideTimer_ invalidate];
       hideTimer_.reset(
@@ -462,31 +483,36 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
 }
 
 - (void)setMenuBarRevealProgress:(CGFloat)progress {
+  // TODO: What happens if a mouse quickly bounces between two screens? What we
+  // really want to know is whether the callback is for the screen that the
+  // browser window is on. I'm not sure what the "progress > menubarFraction_"
+  // check is for but it seems wrong?
   // If the menubarFraction increases, check if we are in the right screen
   // so that the toolbar is not revealed on the wrong screen.
   if (![self isMouseOnScreen] && progress > menubarFraction_)
     return;
 
-  BOOL isMenuBarDisappearing = progress < menubarFraction_;
-  menubarFraction_ = progress;
-
-  if (self.slidingStyle == fullscreen_mac::OMNIBOX_TABS_HIDDEN) {
-    shouldShowToolbarWithoutMenu_ =
-        shouldShowToolbarWithoutMenu_ ||
-        (isMenuBarDisappearing && [self isToolbarFocused]);
-
-    if (IsCGFloatEqual(menubarFraction_, kShowFraction)) {
-      [self setupTrackingArea];
-      hiddenToolbarState_ = fullscreen_mac::TOOLBAR_SHOWN;
+  if (IsCGFloatEqual(menubarFraction_, kShowFraction)) {
+    // NSMenubar fully showing.
+    menubarState_ = fullscreen_mac::MENUBAR_SHOWN;
+  } else if (IsCGFloatEqual(menubarFraction_, kShowFraction)) {
+    // NSMenubar fully hidden.
+    menubarState_ = fullscreen_mac::MENUBAR_HIDDEN;
+  } else {
+    menubarState_ = fullscreen_mac::MENUBAR_TRANSITIONING;
+    menubarAnimatingIn_ = progress > menubarFraction_;
+    if (IsCGFloatEqual(menubarFraction_, kHideFraction) && menubarAnimatingIn_) {
+      // TODO: What if toolbar was animating when menubar starts animating in?
+      // We need to decide what behavior we want. I think we want to override
+      // the existing animation, so this should be toolbarFraction > 0.
+      wasToolbarShowingWhenMenubarStartedAnimatingIn_ = IsCGFloatEqual([self toolbarFraction], kShowFraction);
     }
+  }
+  menubarFraction_ = progress;
 
-    // If |shouldShowToolbarWithoutMenu_| is true, then |hiddenToolbarState_|
-    // should remain fullscreen_mac::TOOLBAR_SHOWN.
-    if (!shouldShowToolbarWithoutMenu_) {
-      hiddenToolbarState_ = IsCGFloatEqual(menubarFraction_, kHideFraction)
-                                ? fullscreen_mac::TOOLBAR_HIDDEN
-                                : fullscreen_mac::TOOLBAR_TRANSITIONING;
-    }
+  if (self.slidingStyle == fullscreen_mac::OMNIBOX_TABS_HIDDEN &&
+      menubarState_ == fullscreen_mac::MENUBAR_SHOWN) {
+    [self setupTrackingArea];
   }
 
   // If an animation is not running, then -layoutSubviews will not be called
@@ -609,7 +635,6 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
   [self removeTrackingAreaIfNecessary];
 
   [currentAnimation_ startAnimation];
-  hiddenToolbarState_ = fullscreen_mac::TOOLBAR_TRANSITIONING;
 }
 
 - (void)cancelHideTimer {