3 files changed, 10 insertions, 1 deletions
diff --git a/chrome/browser/cocoa/browser_window_controller.h b/chrome/browser/cocoa/browser_window_controller.h
index ce55ec6..fae4f2b 100644
--- a/chrome/browser/cocoa/browser_window_controller.h
+++ b/chrome/browser/cocoa/browser_window_controller.h
@@ -234,6 +234,8 @@ class TabContents;
 // Closes the tab sheet |window| and potentially shows the next sheet in the
 // tab's sheet queue.
 - (void)removeConstrainedWindow:(ConstrainedWindowMac*)window;
+// Returns NO if constrained windows cannot be attached to this window.
+- (BOOL)canAttachConstrainedWindow;
 
 // Shows or hides the docked web inspector depending on |contents|'s state.
 - (void)updateDevToolsForContents:(TabContents*)contents;
diff --git a/chrome/browser/cocoa/browser_window_controller.mm b/chrome/browser/cocoa/browser_window_controller.mm
index 2d3f258..3face17 100644
--- a/chrome/browser/cocoa/browser_window_controller.mm
+++ b/chrome/browser/cocoa/browser_window_controller.mm
@@ -444,6 +444,10 @@
   [tabStripController_ removeConstrainedWindow:window];
 }
 
+- (BOOL)canAttachConstrainedWindow {
+  return ![previewableContentsController_ isShowingPreview];
+}
+
 - (void)updateDevToolsForContents:(TabContents*)contents {
   [devToolsController_ updateDevToolsForTabContents:contents];
   [devToolsController_ ensureContentsVisible];
diff --git a/chrome/browser/cocoa/constrained_window_mac.mm b/chrome/browser/cocoa/constrained_window_mac.mm
index e063896..3843c50 100644
--- a/chrome/browser/cocoa/constrained_window_mac.mm
+++ b/chrome/browser/cocoa/constrained_window_mac.mm
@@ -69,7 +69,10 @@ void ConstrainedWindowMac::ShowConstrainedWindow() {
   NSWindowController* controller = [browserWindow windowController];
   if (controller != nil) {
     DCHECK([controller isKindOfClass:[BrowserWindowController class]]);
-    Realize(static_cast<BrowserWindowController*>(controller));
+    BrowserWindowController* browser_controller =
+        static_cast<BrowserWindowController*>(controller);
+    if ([browser_controller canAttachConstrainedWindow])
+      Realize(browser_controller);
   }
 }