Create content::WebContentsDestroyedWatcher, use it in many tests.

chrome/chrome_tests.gypi

Index: chrome/chrome_tests.gypi
diff --git a/chrome/chrome_tests.gypi b/chrome/chrome_tests.gypi
index 08d2ef4962a2d3c37bbefd8cc645863eb56061b5..d9689d7c07bf5dcf2a4788def2c72d86862d4dc6 100644
--- a/chrome/chrome_tests.gypi
+++ b/chrome/chrome_tests.gypi
@@ -210,7 +210,6 @@
         'browser/notifications/desktop_notifications_unittest.cc',
         'browser/notifications/desktop_notifications_unittest.h',
         'browser/notifications/notification_browsertest.cc',
-        'browser/printing/print_dialog_cloud_interative_uitest.cc',
         'browser/task_manager/task_manager_browsertest_util.cc',
         'browser/ui/autofill/autofill_popup_controller_interactive_uitest.cc',
         'browser/ui/browser_focus_uitest.cc',
@@ -1897,7 +1896,6 @@
           'sources/': [
             ['exclude', '^browser/extensions/api/cloud_print_private/cloud_print_private_apitest.cc'],
             ['exclude', '^browser/printing/cloud_print/test/.*'],
-            ['exclude', '^browser/printing/print_dialog_cloud_interative_uitest.cc'],
             ['exclude', '^browser/printing/printing_layout_browsertest.cc'],
             ['exclude', '^browser/printing/print_preview_dialog_controller_browsertest.cc'],
             ['exclude', '^browser/ui/webui/print_preview/print_preview_ui_browsertest.cc'],