Add a DM flag to limit the types of Codec decodes

When the flag "simpleCodec" is set to true, we will only decode
to the canvas colortype and to a scale of 1. No SkAndroidCodec or
BRDCodec tests are run. This makes it easier to find the simple
case when running locally.

Clean up some SkImageDecoder references along the way.
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Review URL: https://codereview.chromium.org/1735743003
1 file changed