Fix grey bar when viewing local capture in Google Meet

Meet gives an option to request video quality of 360. Not all cameras
will natively return a height-360 size, so Chrome will go with the
next-biggest capture size, and letterbox-and-scale the video frame.

On the machine where I reproduced this, the media::VideoFrame had the
following attributes.
- visible_rect:0,60 640x360
- natural_size:640x360
- coded_size:640x480

This exposed the following bug in the combination of the functions
VideoResourceUpdater::CreateForSoftwarePlanes and
PaintCanvasVideoRenderer::Copy.
* The function VideoResourceUpdater::CreateForSoftwarePlanes creates a
  resource of size |coded_size|, and expects that
  PaintCanvasVideoRenderer::Copy will populate the |visible_rect|
  sub-rectangle of that resource.
* PaintCanvasVideoRenderer::Copy actually copies not to |visible_rect|,
  but rather to rectangle at (0,0) that has the size of |visible_rect|.

The consequence is that we end up viewing the resource through a
misaligned letterbox.

The fix is is to inline PaintCanvasVideoRenderer::Copy (which is only a
few lines long) in VideoResourceUpdater::CreateForSoftwarePlanes, and
specify the correct destination rectangle.

Also add some comments to clarify the function's behavior. Note that
this behavior was switched in crrev.com/545920.

Bug: 1090435
Change-Id: Icef81728defc0cf46b35180dada5d68f24e6b21d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2318313
Auto-Submit: ccameron <ccameron@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791480}

media/renderers/paint_canvas_video_renderer.h

@@ -61,7 +61,9 @@ class MEDIA_EXPORT PaintCanvasVideoRenderer {
              VideoTransformation video_transformation,
              viz::RasterContextProvider* raster_context_provider);
 
-  // Paints |video_frame| scaled to its visible size on |canvas|.
+  // Paints |video_frame|, scaled to its |video_frame->visible_rect().size()|
+  // on |canvas|. Note that the origin of |video_frame->visible_rect()| is
+  // ignored -- the copy is done to the origin of |canvas|.
   //
   // If the format of |video_frame| is PIXEL_FORMAT_NATIVE_TEXTURE, |context_3d|
   // and |context_support| must be provided.

media/renderers/video_resource_updater.cc

@@ -1015,11 +1015,19 @@ VideoFrameExternalResources VideoResourceUpdater::CreateForSoftwarePlanes(
         SkBitmap sk_bitmap;
         sk_bitmap.installPixels(info, software_resource->pixels(),
                                 info.minRowBytes());
+        // This is software path, so |canvas| and |video_frame| are always
+        // backed by software.
         cc::SkiaPaintCanvas canvas(sk_bitmap);
-
-        // This is software path, so canvas and video_frame are always backed
-        // by software.
-        video_renderer_->Copy(video_frame, &canvas, nullptr);
+        cc::PaintFlags flags;
+        flags.setBlendMode(SkBlendMode::kSrc);
+        flags.setFilterQuality(kLow_SkFilterQuality);
+
+        // Note that PaintCanvasVideoRenderer::Copy would copy to the origin,
+        // not |video_frame->visible_rect|, so call Paint instead.
+        // https://crbug.com/1090435
+        video_renderer_->Paint(video_frame, &canvas,
+                               gfx::RectF(video_frame->visible_rect()), flags,
+                               media::kNoTransformation, nullptr);
       } else {
         HardwarePlaneResource* hardware_resource = plane_resource->AsHardware();
         size_t bytes_per_row = viz::ResourceSizes::CheckedWidthInBytes<size_t>(