Initial pass at integrating Differ into the chromoting host code....

gfx/point.h

Index: gfx/point.h
===================================================================
--- gfx/point.h	(revision 55264)
+++ gfx/point.h	(working copy)
@@ -73,6 +73,16 @@
     return !(*this == rhs);
   }
 
+  // A point is less than another point if its y-value is closer
+  // to the origin. If the y-values are the same, then point with
+  // the x-value closer to the origin is considered less than the
+  // other.
+  // This comparison is required to use Points in sets, or sorted
+  // vectors.
+  bool operator<(const Point& rhs) const {
+    return (y_ == rhs.y_) ? (x_ < rhs.x_) : (y_ < rhs.y_);
+  }
+
 #if defined(OS_WIN)
   POINT ToPOINT() const;
 #elif defined(OS_MACOSX)