How about move |is_encrypted()| method from DecryptConfig to DecoderBuffer?

// call in this unique way
!buffer->is_encrypted()

bool DecoderBuffer::is_encrypted() {
  return decrypt_config_ && !decrypt_config_->key_id_.empty() && !decrypt_config_->iv_.empty();
}

This would work, but part of me feels that if the buffer is not encrypted, we probably should not set the DecryptConfig at all. I'll have to put more thoughts on it.

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Now we'll add EncryptionScheme, and that is another way to check whether a buffer is encrypted. But I still feel #2 is the best solution.

Encrypted buffers won't have a DecryptConfig. CL out for review, but won't land before M68.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9044a767f5066248501ff9806a080c7ab7561f60

commit 9044a767f5066248501ff9806a080c7ab7561f60
Author: John Rummell <jrummell@chromium.org>
Date: Thu Apr 19 01:24:07 2018

Add EncryptionMode and EncryptionPattern to DecryptConfig

In order to support different encryption schemes for protected content,
include the encryption mode and optional pattern in DecryptConfig.

This also changes the way that unencrypted buffers are tagged. They
no longer contain a DecryptConfig if the contents are unencrypted.

Future CLs will enable detection of different schemes as well as passing
it to the CDM.

BUG=657957,658026, 675003 
TEST=existing EME browser_tests pass

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ief02810cfe134e973ec39976277f3209683db612
Reviewed-on: https://chromium-review.googlesource.com/884947
Commit-Queue: John Rummell <jrummell@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Kongqun Yang <kqyang@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551911}
[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/chromecast/media/cma/base/decoder_buffer_adapter.cc
[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/chromecast/media/cma/base/decoder_buffer_adapter_unittest.cc
[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/chromecast/media/cma/test/frame_generator_for_test.cc
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[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/media/formats/webm/webm_crypto_helpers_unittest.cc
[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/media/gpu/android/codec_wrapper.cc
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[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/media/remoting/proto_enum_utils.cc
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[modify] https://crrev.com/9044a767f5066248501ff9806a080c7ab7561f60/media/remoting/rpc.proto

buffer->decrypt_config() is null if the buffer is not encrypted and DecryptConfig::is_encrypted() is gone. Can't create a DecryptConfig for unencrypted content.