Fix crash in WebContentsViewAura::WindowObserver that happens when switching tabs. The exact repro …

chrome/browser/ui/webui/print_preview/print_preview_ui_browsertest.cc

Index: chrome/browser/ui/webui/print_preview/print_preview_ui_browsertest.cc
===================================================================
--- chrome/browser/ui/webui/print_preview/print_preview_ui_browsertest.cc	(revision 235277)
+++ chrome/browser/ui/webui/print_preview/print_preview_ui_browsertest.cc	(working copy)
@@ -141,6 +141,22 @@
       region_before.bottom == region_after.bottom;
   ASSERT_FALSE(rects_equal);
 }
+
+IN_PROC_BROWSER_TEST_F(PrintPreviewTest, NoCrashOnCloseWithOtherTabs) {
+  // Now print preview.
+  Print();
+
+  ui_test_utils::NavigateToURLWithDisposition(
+      browser(), GURL("about:blank"), NEW_FOREGROUND_TAB,
+      ui_test_utils::BROWSER_TEST_WAIT_FOR_NAVIGATION);
+
+  browser()->tab_strip_model()->ActivateTabAt(0, true);
+
+  // Navigate main tab to hide print preview.
+  ui_test_utils::NavigateToURL(browser(), GURL("about:blank"));
+
+  browser()->tab_strip_model()->ActivateTabAt(1, true);
+}
 #endif
 
 }  // namespace