Commits on Jun 2, 2015

1. Improve the stability of tests run using WebDriver. …

   * Wait for the correct pipeline to return a LoadComplete message
     before signalling a load is complete, and ensure that the root
     pipeline is the one corresponding to the active document of the top
     level browsing context, even if this has not yet painted.
   
   * Ensure that TakeScreenshot operates on the correct pipeline
   
   * Reset the screenshot ready flag whenever we decide that we are ready
     to take a screenshot.

   

   jgraham committed Jun 2, 2015

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