Restore r25049 (back out r25295) to isolate it as the cause of bug 20872

chrome/browser/cocoa/tab_strip_controller.mm

Index: chrome/browser/cocoa/tab_strip_controller.mm
===================================================================
--- chrome/browser/cocoa/tab_strip_controller.mm	(revision 25295)
+++ chrome/browser/cocoa/tab_strip_controller.mm	(working copy)
@@ -419,8 +419,10 @@
         tabFrame.origin.x = offset;
       }
 
-      // Animate the tab in by putting it below the horizon.
-      if (newTab && visible && animate) {
+      // Animate the tab in by putting it below the horizon, but don't bother
+      // if we only have 1 tab.
+      BOOL shouldAnimate = animate && [tabContentsArray_ count] > 1;
+      if (newTab && visible && shouldAnimate) {
         [[tab view] setFrame:NSOffsetRect(tabFrame, 0, -NSHeight(tabFrame))];
       }
 
@@ -449,7 +451,8 @@
   }
 
   // Hide the new tab button if we're explicitly told to. It may already
-  // be hidden, doing it again doesn't hurt.
+  // be hidden, doing it again doesn't hurt. Otherwise position it
+  // appropriately, showing it if necessary.
   if (forceNewTabButtonHidden_) {
     [newTabButton_ setHidden:YES];
   } else {
@@ -461,10 +464,8 @@
     newTabNewFrame.origin.x = MAX(newTabNewFrame.origin.x,
                                   NSMaxX(placeholderFrame_)) +
                                       kNewTabButtonOffset;
-    if (i > 0 && [newTabButton_ isHidden]) {
-      id target = animate ? [newTabButton_ animator] : newTabButton_;
-      [target setHidden:NO];
-    }
+    if ([tabContentsArray_ count])
+      [newTabButton_ setHidden:NO];
 
     if (!NSEqualRects(newTabTargetFrame_, newTabNewFrame)) {
       [newTabButton_ setFrame:newTabNewFrame];