16 bpp video stream capture, render and createImageBitmap(video) using (CPU) shared memory buffers

cc/resources/video_resource_updater.cc

Index: cc/resources/video_resource_updater.cc
diff --git a/cc/resources/video_resource_updater.cc b/cc/resources/video_resource_updater.cc
index 4c6b21619b2de28f55d5e6f1aeb935a028326d36..82201607726dcdf0c68f348328dc5422ab54db1a 100644
--- a/cc/resources/video_resource_updater.cc
+++ b/cc/resources/video_resource_updater.cc
@@ -428,11 +428,9 @@ VideoFrameExternalResources VideoResourceUpdater::CreateForSoftwarePlanes(
       break;
   }
 
-  // TODO(dshwang): support PIXEL_FORMAT_Y16. crbug.com/624436
-  DCHECK_NE(bits_per_channel, 16);
-
-  // Only YUV software video frames are supported.
-  if (!media::IsYuvPlanar(input_frame_format)) {
+  // Only YUV and Y16 software video frames are supported.
+  const bool isYuvPlanar = media::IsYuvPlanar(input_frame_format);

[danakj, 2016/10/24 21:46:37]

use chromium style please for isYuvPlanar

[aleksandar.stojiljkovic, 2016/10/25 10:12:28]

Done.

+  if (!(isYuvPlanar || input_frame_format == media::PIXEL_FORMAT_Y16)) {
     NOTREACHED() << media::VideoPixelFormatToString(input_frame_format);

[danakj, 2016/10/24 21:46:37]

Hm where did this NOTREACHED();return; come from? Can you turn this into a
DCHECK instead and drop the return

Or, drop the NOTREACHED if the DCHECK would occur (I hope not?) 

[aleksandar.stojiljkovic, 2016/10/25 10:12:28]

NOTREACHED();return; is there from previous code; NOTREACHED contributed in [1]
and "return" even earlier.

[1]
https://chromium.googlesource.com/chromium/src/+/7a6c2a346104a0269767c7174d09...

Check is useful, when someone adds a new format like me here, existing tests
triggered NOTREACHED. So, DCHECK is good.

However, that is an orthogonal change (unnecessary risk) to this patch - propose
to add it in separate patch: https://crrev.com/2447013002/  

     return VideoFrameExternalResources();
   }
@@ -440,7 +438,8 @@ VideoFrameExternalResources VideoResourceUpdater::CreateForSoftwarePlanes(
   const bool software_compositor = context_provider_ == NULL;
 
   ResourceFormat output_resource_format =
-      resource_provider_->YuvResourceFormat(bits_per_channel);
+      isYuvPlanar ? resource_provider_->YuvResourceFormat(bits_per_channel)
+                  : ResourceFormat::RGBA_8888;

[danakj, 2016/10/24 21:46:37]

Can you leave a comment explaining this in the context of the above DCHECK
because I spent some time here being confused. Specifically, if not yuv-planar
then it is PIXEL_FORMAT_Y16 which will use RGBA_8888. Alternatively, restructure
this to have the code explain it better. Perhaps like

if (input_frame_format == ..Y16) {
  // Unable to display directly as yuv planes so convert it to RGBA for
compositing.
  output_resource_format = RGBA_888
} else {
  // Can be composited directly from yuv planes.
  output_resource_format = r_p_->YuvRF(..bits..);
}

[aleksandar.stojiljkovic, 2016/10/25 10:12:28]

Done. Thanks.

 
   // If GPU compositing is enabled, but the output resource format
   // returned by the resource provider is RGBA_8888, then a GPU driver