tools/android/loading: Implements CacheBackend.GetDecodedContentForKey()
tools/android/loading: Implements CacheBackend.GetDecodedContentForKey()

HTTP cache is storing into key's index stream 1 the transport layer
resource binary. However, the resources might be encoded using a
compression algorithm specified in the Content-Encoding response
header. This new method takes care of returning decoded binary
content of the resource if necessary.

BUG=582080

Review URL: https://codereview.chromium.org/1765033002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#382625}

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