[linux] remove dependency between nacl_helper and media

[linux] remove dependency between nacl_helper and media

nacl_helper depends on //content/common which depends on //media. That's
why nacl_helper cannot start without libffmpeg.so. This commit removes
such dependency adding target //content/common:sandbox_linux

R=mseaborn@chromium.org,piman@chromium.org
BUG=642306

[Mark Seaborn, 2016-08-31 18:28:04]

https://codereview.chromium.org/2297993003/diff/1/content/common/BUILD.gn
File content/common/BUILD.gn (right):

https://codereview.chromium.org/2297993003/diff/1/content/common/BUILD.gn#new...
content/common/BUILD.gn:233:
"//content/public/common/child_process_sandbox_support_linux.h",
This is duplicating too much in the GN build to handle a case that's not tested
by the Chromium bots (i.e. overriding libffmpeg via LD_LIBRARY_PATH).

Can you find a simpler way to achieve this?

For example, content_switches.cc is currently referenced by
content/public/common/BUILD.gn.  It's not good to be adding a reference to a
different BUILD.gn file.  But content/public/common/BUILD.gn already defines a
separate target for it, so you can reference that target rather than duplicating
the reference here.

Maybe you could do the same for the other files?  Where are these other files
currently referenced from?  What currently pulls in the media dependency that
you want to remove?

[rkuksin, 2016-09-01 05:46:55]

> Maybe you could do the same for the other files?  

I referenced //content/public/common:static_switches and removed few files from
the target.
The other files have no separate targets we can use, so we can't do the same.

> Where are these other files
> currently referenced from?  What currently pulls in the media dependency that
> you want to remove?

They are referenced from //content/common or //content/public/common both
dependent on //media.
New target //content/common:sandbox_linux duplicates sandbox related files from
these two targets.

I don't see a simpler way to remove the dependency.

[Mark Seaborn, 2016-09-08 20:46:55]

https://codereview.chromium.org/2297993003/diff/20001/content/common/BUILD.gn
File content/common/BUILD.gn (right):

https://codereview.chromium.org/2297993003/diff/20001/content/common/BUILD.gn...
content/common/BUILD.gn:233:
"//content/public/common/child_process_sandbox_support_linux.h",
I'm afraid this is still duplicating more than I am comfortable with.  I
wouldn't want to give other people the burden of maintaining this.

Does my suggestion in https://crbug.com/642306 work for you instead?

[rkuksin, 2016-09-09 12:09:32]

On 2016/09/08 20:46:55, Mark Seaborn wrote:
> https://codereview.chromium.org/2297993003/diff/20001/content/common/BUILD.gn
> File content/common/BUILD.gn (right):
> 
>
https://codereview.chromium.org/2297993003/diff/20001/content/common/BUILD.gn...
> content/common/BUILD.gn:233:
> "//content/public/common/child_process_sandbox_support_linux.h",
> I'm afraid this is still duplicating more than I am comfortable with.  I
> wouldn't want to give other people the burden of maintaining this.
> 
> Does my suggestion in https://crbug.com/642306 work for you instead?

Yes, it works
Thanks