Update sink wants with ranges for both pixel count and frame rate.

webrtc/media/base/videosourceinterface.h

Index: webrtc/media/base/videosourceinterface.h
diff --git a/webrtc/media/base/videosourceinterface.h b/webrtc/media/base/videosourceinterface.h
index 0ea1c60abfa389e5bc236925e25d9bae74e2886d..7ac212bd7557edb5a5c6bb1558e504cfb3e282e6 100644
--- a/webrtc/media/base/videosourceinterface.h
+++ b/webrtc/media/base/videosourceinterface.h
@@ -26,14 +26,43 @@ struct VideoSinkWants {
   // Tells the source that the sink only wants black frames.
   bool black_frames = false;
 
-  // Tells the source the maximum number of pixels the sink wants.
-  rtc::Optional<int> max_pixel_count;
+  // Indicates a range some value should be constrained to, such as resolution
+  // (pixel count) or frame rate. It is up to the application code to make sure
+  // |min| <= |target| <= |max|.
+  struct Range {
+    Range()
+        : min(0), target(std::numeric_limits<uint32_t>::max()), max(target) {}
+    Range(uint32_t min, uint32_t target, uint32_t max)
+        : min(min), target(target), max(max) {}
+
+    // |min| = 0, indicates no lower bound.
+    uint32_t min;
+    // |target| = maxint by default - requesting highest option available.
+    uint32_t target;
+    // |max| = maxint, indicates to upper bound.
+    uint32_t max;
+  };
+
   // Tells the source the desired number of pixels the sinks wants. This will
-  // typically be used when stepping the resolution up again when conditions
-  // have improved after an earlier downgrade. The source should select the
-  // closest resolution to this pixel count, but if max_pixel_count is set, it
-  // still sets the absolute upper bound.
-  rtc::Optional<int> target_pixel_count;
+  // typically be used when stepping the resolution down or up again as resource
+  // constraints are imposed or lifted.
+  //
+  // For example, when stepping down resolution on CPU overuse, it's preferable
+  // to set the max just below the current resolution but the target to a
+  // resolution that it is assumed would result in a utilization the system can
+  // handle. The source should select a resolution as close to |target| as
+  // possible, but no higher than |max|. Then |min| limit can then be set so
+  // that user requested minimum resolution bounds aren't violated.
+  //
+  // Similarly, when stepping up again, the |min| limit can be set one higher
+  // than the current resolution, and |target| to something reasonably higher
+  // (probably matching the step size down). The |max| limit can be set to
+  // avoid too large input.
+  rtc::Optional<Range> pixel_count;
+
+  // These constraints work in just the same manner as the pixel_count ones, but
+  // instead of limiting resolution they limit the framerate.
+  rtc::Optional<Range> framerate_fps_;
 };
 
 template <typename VideoFrameT>