Bug 925892: add "channel=searchbar" parameter to Google plugin to distinguish search bar searches, r=MattN

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extra : transplant_source : %CD%D4%0BqxCt%82%BA%80%CE%E6%C3%E1%F3V%96xo%81
Bug 925898: properly pass the "homepage" reason to getSubmission calls for about:home, r=MattN

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extra : transplant_source : %10i%ADC%D2W%C0%C0%99LM%9AR%D3%09%B29%10%F1%25