add video hole support to the gn build

build/config/features.gni

Index: build/config/features.gni
diff --git a/build/config/features.gni b/build/config/features.gni
index db70755e884cce953bd450c598274a8c1f0a5a6c..0292ddb06016721918e2e20ca46fe5df79489b1e 100644
--- a/build/config/features.gni
+++ b/build/config/features.gni
@@ -74,6 +74,9 @@ declare_args() {
   enable_one_click_signin = is_win || is_mac || (is_linux && !is_chromeos)
 
   enable_remoting = !is_ios && !is_android
+
+  # Should we enable hole punching for protected video?

[tfarina, 2015/03/31 16:17:06]

I tend to prefer to keep this comment equal to the GYP version, just changing
'Set to 1' to 'Set to true'...

[Mostyn Bramley-Moore, 2015/03/31 16:25:20]

I reworded this to improve the grammar.  Would you prefer my version be added to
build/common.gypi or that version here instead?

[Mostyn Bramley-Moore, 2015/04/01 07:52:43]

I changed this to be the same as the gyp comment.  We can fix both later if you
like.

+  enable_video_hole = is_android

[tfarina, 2015/03/31 16:17:07]

Should this be = false? How GYP enables this? It seems to be set to 0 there.

[Mostyn Bramley-Moore, 2015/03/31 16:25:20]

build/common.gypi has defaults for this in three places...

line 624 (not inside a condition AFAICT): default to 0
line 778: (inside an OS=="android" condition): default to 1
line 1844: (inside a chromecast==1 condition): default to 1

I couldn't find a chromecast gn variable or argument.

 }
 
 # Additional dependent variables -----------------------------------------------