Fullscreen tab capture: Prefer standard resolutions

content/browser/media/capture/web_contents_video_capture_device.cc

Index: content/browser/media/capture/web_contents_video_capture_device.cc
diff --git a/content/browser/media/capture/web_contents_video_capture_device.cc b/content/browser/media/capture/web_contents_video_capture_device.cc
index d90cbd1891668dfa502b55118a22060e5cd0bc80..41fa280b04c69bb173de6ed5479bb298c7a39112 100644
--- a/content/browser/media/capture/web_contents_video_capture_device.cc
+++ b/content/browser/media/capture/web_contents_video_capture_device.cc
@@ -642,6 +642,43 @@ gfx::Size WebContentsCaptureMachine::ComputeOptimalViewSize() const {
   // http://crbug.com/350491
   gfx::Size optimal_size = oracle_proxy_->max_frame_size();
 
+  switch (capture_params_.resolution_change_policy) {
+    case media::RESOLUTION_POLICY_FIXED_RESOLUTION:
+      break;
+    case media::RESOLUTION_POLICY_FIXED_ASPECT_RATIO:
+    case media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT: {
+      // If the max frame size is close to a common video aspect ratio, compute
+      // a standard resolution for that aspect ratio.  For example, given
+      // 1365x768, which is very close to 16:9, the optimal size would be
+      // 1280x720.  The purpose of this logic is to prevent scaling quality
+      // issues caused by "one pixel stretching" and/or odd-to-even dimension
+      // scaling, and to improve the performance of consumers of the captured
+      // video.
+      const auto HasIntendedAspectRatio =
+          [](const gfx::Size& size, int width_units, int height_units) {
+        const int a = height_units * size.width();
+        const int b = width_units * size.height();
+        const int percentage_diff = 100 * std::abs((a - b)) / b;
+        return percentage_diff <= 1;  // Effectively, anything strictly <2%.
+      };
+      const auto RoundToExactAspectRatio =
+          [](const gfx::Size& size, int width_step, int height_step) {
+        const int adjusted_height =
+            std::max(size.height() - (size.height() % height_step),
+                     height_step);
+        DCHECK_EQ((adjusted_height * width_step) % height_step, 0);
+        return gfx::Size(adjusted_height * width_step / height_step,
+                         adjusted_height);
+      };
+      if (HasIntendedAspectRatio(optimal_size, 16, 9))
+        optimal_size = RoundToExactAspectRatio(optimal_size, 160, 90);
+      else if (HasIntendedAspectRatio(optimal_size, 4, 3))
+        optimal_size = RoundToExactAspectRatio(optimal_size, 64, 48);
+      // Else, do not make an adjustment.
+      break;
+    }
+  }
+
   // If the ratio between physical and logical pixels is greater than 1:1,
   // shrink |optimal_size| by that amount.  Then, when external code resizes the
   // render widget to the "preferred size," the widget will be physically