[Material][Mac] Fix tabstrip and avatar button hierarchy

BUG=620614

Review-Url: https://codereview.chromium.org/2091873002
Cr-Commit-Position: refs/heads/master@{#402687}

chrome/browser/ui/cocoa/browser_window_controller.mm

@@ -1912,6 +1912,10 @@ willAnimateFromState:(BookmarkBar::State)oldState
   return [presentationModeController_ menubarOffset];
 }
 
+- (NSView*)avatarView {
+  return [avatarButtonController_ view];
+}
+
 - (void)enterWebContentFullscreen {
   // HTML5 Fullscreen should only use AppKit fullscreen in 10.10+.
   // However, if the user is using multiple monitors and turned off

chrome/browser/ui/cocoa/tabs/tab_window_controller.h

@@ -159,6 +159,9 @@
 // the screen (tab strip, omnibox, bookmark bar, etc). Ranges from 0 to -22.
 - (CGFloat)menubarOffset;
 
+// Returns the view of the avatar button.
+- (NSView*)avatarView;
+
 // Tell the window that it needs to call performClose: as soon as the current
 // drag is complete. This prevents a window (and its overlay) from going away
 // during a drag.

chrome/browser/ui/cocoa/tabs/tab_window_controller.mm

@@ -182,15 +182,15 @@
     // Return the original window's tab strip view and content view to their
     // places. The TabStripView always needs to be in front of the window's
     // content view and therefore it should always be added after the content
-    // view is set. It needs to be positioned at the bottom of the view
-    // hierarchy to ensure that it does not overlap the avatar button icon.
+    // view is set. It needs to be positioned below the avatar button to ensure
+    // that its overlay will not overlap it.
     [[window contentView] addSubview:originalContentView_
                           positioned:NSWindowBelow
                           relativeTo:nil];
     originalContentView_.frame = [[window contentView] bounds];
     [[window contentView] addSubview:[self tabStripView]
                           positioned:NSWindowBelow
-                          relativeTo:nil];
+                          relativeTo:[self avatarView]];
     [[self tabStripView] setInATabDraggingOverlayWindow:NO];
     [[window contentView] updateTrackingAreas];
 
@@ -315,6 +315,10 @@
   return 0;
 }
 
+- (NSView*)avatarView {
+  return nil;
+}
+
 - (NSString*)activeTabTitle {
   // subclass must implement
   NOTIMPLEMENTED();