Our tests are linked with gunit_main (or gunit_main_no_google3), which means that main is already defined in another translation unit. Having two main functions violates ODR and hence can result in undefined behavior.

There is no need to fear losing tests. If a build system tries to run a test and there is no main function, then it will fail. Hence, i cannot see a way for this to stop testing a test.

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Also putting all subtle-classes in namespace crypto::tink::subtle.

Change-Id: I47fece5df4ef524521449320d619b13ba8466373
ORIGINAL_AUTHOR=Bartosz Przydatek <przydatek@google.com>
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Change-Id: Ib1af3c9b6d297d45df29cf09de74ebc0a6e9bebe
ORIGINAL_AUTHOR=Thai Duong <thaidn@google.com>
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ORIGINAL_AUTHOR=Thai Duong <thaidn@google.com>
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