Bug 834165 - Implement BlobEvent. r=smaug

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extra : rebase_source : 5d8f13baa4b2ff00a63300be54edb81ab2555bd9
Bug 836655 - [Audio] Remove ChildID if there is no content channel playing in foreground and only send audio-channel-changed with normal when ChildID in the background has content channel in playing state. r=baku

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extra : rebase_source : 7c047f8643ca32920128fac51f92eb50dd1f4e30