Implement all resolution change policies for desktop and tab capture.

content/browser/media/capture/capture_resolution_chooser.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_MEDIA_CAPTURE_CAPTURE_RESOLUTION_CHOOSER_H_
+#define CONTENT_BROWSER_MEDIA_CAPTURE_CAPTURE_RESOLUTION_CHOOSER_H_
+
+#include "content/common/content_export.h"
+#include "media/base/video_capture_types.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace content {
+
+// Encapsulates the logic that determines the capture frame resolution based on:
+//   1. The configured maximum frame resolution and resolution change policy.
+//   2. The resolution of the source content.
+//   3. The current capabilities of the end-to-end system, in terms of the
+//      maximum number of pixels per frame.
+class CONTENT_EXPORT CaptureResolutionChooser {
+ public:
+  // media::ResolutionChangePolicy determines whether the variable frame
+  // resolutions being computed must adhere to a fixed aspect ratio or not, or
+  // that there must only be a single fixed resolution.
+  CaptureResolutionChooser(
+      const gfx::Size& max_frame_size,
+      media::ResolutionChangePolicy resolution_change_policy);
+  ~CaptureResolutionChooser();
+
+  // Returns the current capture frame resolution to use.
+  gfx::Size capture_size() const {
+    return capture_size_;
+  }
+
+  // Updates the capture size based on a change in the resolution of the source
+  // content.
+  void SetSourceSize(const gfx::Size& source_size);
+
+ private:
+  // Called after any update that requires |capture_size_| be re-computed.
+  void RecomputeCaptureSize();
+
+  // Hard constraints.
+  const gfx::Size max_frame_size_;
+  const gfx::Size min_frame_size_;  // Computed from the ctor arguments.
+
+  // Specifies the set of heuristics to use.
+  const media::ResolutionChangePolicy resolution_change_policy_;
+
+  // The capture frame resolution to use, ignoring the limitations imposed by
+  // the capability metric.
+  gfx::Size constrained_size_;
+
+  // The current computed capture frame resolution.
+  gfx::Size capture_size_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_CAPTURE_RESOLUTION_CHOOSER_H_