mac: Fix flickering of install extension window.

chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.mm

Index: chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.mm
diff --git a/chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.mm b/chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.mm
index 3bb3f4bfb78449782f544a1d1a50743ce9b0fba8..dea0ceff5e61359d0c4a127c900f5cca11c0e14f 100644
--- a/chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.mm
+++ b/chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.mm
@@ -25,7 +25,9 @@ const NSTimeInterval kAnimationDuration = 0.18;
 
 - (void)showSheetForWindow:(NSWindow*)window {
   base::scoped_nsobject<NSAnimation> animation;
-  if (!useSimpleAnimations_) {
+  if (useSimpleAnimations_) {
+    [customWindow_ setAlphaValue:0.0];
+  } else {
     animation.reset(
         [[ConstrainedWindowAnimationShow alloc] initWithWindow:customWindow_]);
   }
@@ -36,7 +38,6 @@ const NSTimeInterval kAnimationDuration = 0.18;
   [customWindow_ makeKeyAndOrderFront:nil];
 
   if (useSimpleAnimations_) {
-    [customWindow_ setAlphaValue:0.0];
     [NSAnimationContext beginGrouping];
     [[NSAnimationContext currentContext] setDuration:kAnimationDuration];
     [[customWindow_ animator] setAlphaValue:1.0];