mac: Fix a logic error in presentation_mode_controller.

The method -shouldShowMenubarInImmersiveFullscreen failed to take into
consideration whether the screen containing the window had a menu bar.

BUG=NONE
TEST=On OSX 10.9 or OSX 10.10, set the screensHaveSeparateSpaces setting to NO.
On a second monitor, fullscreen a youtube video. Move the mouse to the top of
screen. The tabstrip should appear, and should not have extra space for a menu
bar. Prior to this CL, there would be extra space for a non-existent menu bar.

Review URL: https://codereview.chromium.org/645643004

Cr-Commit-Position: refs/heads/master@{#299011}

chrome/browser/ui/cocoa/presentation_mode_controller.mm

@@ -180,8 +180,8 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
 - (void)showActiveWindowUI;
 - (void)hideActiveWindowUI;
 
-// In Immersive Fullscreen, the menubar is visible iff. toolbarFraction_ >=
-// 1.0.
+// Whether the menu bar should be shown in immersive fullscreen for the screen
+// that contains the window.
 - (BOOL)shouldShowMenubarInImmersiveFullscreen;
 
 @end
@@ -745,7 +745,7 @@ OSStatus MenuBarRevealHandler(EventHandlerCallRef handler,
 }
 
 - (BOOL)shouldShowMenubarInImmersiveFullscreen {
-  return toolbarFraction_ >= 1.0;
+  return [self doesScreenHaveMenuBar] && toolbarFraction_ > 0.99;
 }
 
 @end