Work around a clang/win bug, add a .h file to gyp/gn files.

Work around a clang/win bug, add a .h file to gyp/gn files.

clang can't handle dllexported classes with only member initializers yet
(see crbug and http://llvm.org/PR23542). As a workaround, don't dllexport
this class.  This has the effect of emitting the class's constructor into
every translation unit that uses it instead of just every translation unit of
the media component, but in a way that seems nicer anyways since there's no
.cc file for this header and so currently this relies on some translation unit
in media including this header by lucky accident (else the constructor wouldn't
be defined anywhere.)

Once the clang bug is fixed we can consider adding this back; in the meantime
this seems like a tiny price to pay to get the bots back green.

Also add the .h file to the relevant gyp/gn files, else the analyze
step will make the trybots think that nothing changed when this
.h file is touched.

BUG=488634, 467779
TBR=sandersd

Committed: https://crrev.com/8a0f0753b1ece73c5636b263f4c4a13f75fcb2cd
Cr-Commit-Position: refs/heads/master@{#330299}

[Nico, 2015-05-17 02:21:01]

thakis@chromium.org changed reviewers:
+ hans@chromium.org, sandersd@chromium.org

[Nico, 2015-05-17 03:26:58]

I'll tbr this to get the bots back green.

[Nico, 2015-05-17 03:27:12]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-05-17 03:27:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1133423003/20001

[Nico, 2015-05-17 03:27:28]

(But please do give it a look when you get the chance!)

[commit-bot: I haz the power, 2015-05-17 03:31:02]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-18 11:32:24]

Patchset 2 (id:??) landed as
https://crrev.com/8a0f0753b1ece73c5636b263f4c4a13f75fcb2cd
Cr-Commit-Position: refs/heads/master@{#330299}

[hans, 2015-05-18 16:16:44]

lgtm

Thanks for fixing this. I'll try to get to the Clang bug this week.

[sandersd (OOO until July 31), 2015-05-18 18:01:49]

lgtm