I just got this crash on trunk (r506341) when tapping on a search result in the contextual search overlay:

java.lang.AssertionError: clobberCurrentTab was called with an empty tab.
  at org.chromium.chrome.browser.externalnav.ExternalNavigationDelegateImpl.clobberCurrentTab(ExternalNavigationDelegateImpl.java:519)
  at org.chromium.chrome.browser.externalnav.ExternalNavigationHandler.clobberCurrentTabWithFallbackUrl(ExternalNavigationHandler.java:626)
  at org.chromium.chrome.browser.externalnav.ExternalNavigationHandler.shouldOverrideUrlLoadingInternal(ExternalNavigationHandler.java:362)
  at org.chromium.chrome.browser.externalnav.ExternalNavigationHandler.shouldOverrideUrlLoading(ExternalNavigationHandler.java:130)
  at org.chromium.chrome.browser.contextualsearch.ContextualSearchManager$SearchOverlayContentDelegate.shouldInterceptNavigation(ContextualSearchManager.java:1029)
  at org.chromium.chrome.browser.compositor.bottombar.OverlayPanelContent$InterceptNavigationDelegateImpl.shouldIgnoreNavigation(OverlayPanelContent.java:121)
  at org.chromium.base.SystemMessageHandler.nativeDoRunLoopOnce(Native Method)
  at org.chromium.base.SystemMessageHandler.handleMessage(SystemMessageHandler.java:52)
  at android.os.Handler.dispatchMessage(Handler.java:102)
  at android.os.Looper.loop(Looper.java:154)
  at android.app.ActivityThread.main(ActivityThread.java:6121)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)