Add heuristics to limit showing of new backspace UI bubble.

chrome/test/base/test_browser_window.cc

Index: chrome/test/base/test_browser_window.cc
diff --git a/chrome/test/base/test_browser_window.cc b/chrome/test/base/test_browser_window.cc
index de299f63a2043309d277173b5d583acbf27191d6..29e4164aaf734b366a3ce007a975ab733746d655 100644
--- a/chrome/test/base/test_browser_window.cc
+++ b/chrome/test/base/test_browser_window.cc
@@ -119,8 +119,6 @@ bool TestBrowserWindow::IsFullscreenBubbleVisible() const {
   return false;
 }
 
-void TestBrowserWindow::ShowNewBackShortcutBubble(bool forward) {}
-
 LocationBar* TestBrowserWindow::GetLocationBar() const {
   return const_cast<TestLocationBar*>(&location_bar_);
 }