[chrome.displaySource] Implement software based H.264 video encoder.

extensions/extensions.gyp

Index: extensions/extensions.gyp
diff --git a/extensions/extensions.gyp b/extensions/extensions.gyp
index 3aae4cb258e6b603f96fce52096d3a347125aac4..f2ee014ae9817c26203053780131b3a33e78cb21 100644
--- a/extensions/extensions.gyp
+++ b/extensions/extensions.gyp
@@ -226,6 +226,14 @@
           'sources': [
             '<@(extensions_renderer_sources_wifi_display)',
           ],
+          'conditions': [
+            ['use_openh264==1', {

[hbos_chromium, 2016/04/28 09:02:33]

I added the use_openh264 flag so that I could control if openh264 is build in
chromium. While writing the build files for third_party/openh264 I changed the
default value of use_openh264 to true to make sure it built on the bots (and
then changed back to false before landing).

I don't know about enable_wifi_display, but I don't think any bots override
use_openh264, which means your code is not getting tested by our bots. This flag
is so far not used for anything except adding a dependency to the All targets
(which is probably a dependency I should remove now that the build files are
healthy, only targets using the library should have a direct dependency on it,
such as this one).

I was going to use the flag, but for the third_party/webrtc encoder using
openh264 that I wrote (h264_encoder_impl.cc) I had to use a flag defined in the
webrtc repo instead (rtc_use_h264). We made this flag default to
proprietary_codecs, which is used in Chrome Official build and other bots.

You probably want to use a flag that defaults to proprietaty_codecs too? You
could modify use_openh264 to default to proprietary_codecs or create a new flag
that defaults to it. That way your code is used without extra flags.

I'm debating removing use_openh264 since even if its false openh264 could be
used (if rtc_use_h264=1); confusing.

[hbos_chromium, 2016/04/28 09:22:15]

If this does not apply because this is an extension and you don't mind the extra
flag you can leave this as-is. I don't know the background.

[e_hakkinen, 2016/04/28 13:47:39]

The code is not used without an extra flags anyway as enable_wifi_display is
false by default.

As the software fallback is quite important part of WiFi Display stack, I just
removed the condition altogether.

[hbos_chromium, 2016/04/28 14:27:29]

There are reasons for why third_party/openh264 is not built by default. We need
to be careful about adding dependency on it without special flags. It is already
behind one flag, but I think you should add a new flag and default it to
proprietary_codecs, making openh264 an optional part of this extension.

+              'defines': ['USE_OPENH264=1'],
+              'dependencies': [
+                '../third_party/openh264/openh264.gyp:openh264_encoder',
+              ]
+            }]
+          ]
         }],
       ],
     },