Handle large rects better.

ui/gfx/geometry/rect.cc

Index: ui/gfx/geometry/rect.cc
diff --git a/ui/gfx/geometry/rect.cc b/ui/gfx/geometry/rect.cc
index f3c47b2b378e9b0bd8087330560a4b7541e6384d..1ebe16991f691ecc7f736bfff5f6c31f458f981e 100644
--- a/ui/gfx/geometry/rect.cc
+++ b/ui/gfx/geometry/rect.cc
@@ -157,8 +157,29 @@ void Rect::Union(const Rect& rect) {
   int rb = std::max(bottom(), rect.bottom());
 
   // Subtracting to get width/height might overflow integers, so clamp them.
-  SetRect(rx, ry, base::SaturatedSubtraction(rr, rx),
-          base::SaturatedSubtraction(rb, ry));
+  int rdx = base::SaturatedSubtraction(rr, rx);
+  int rdy = base::SaturatedSubtraction(rb, ry);
+
+  // clamping may move one side, choose to move the bigger by recomputing it.
+  // The computation of right is implicit, so this happens vacuosly.
+  //  If Right is small, move left to width away.
+  //  If Left is big(negative), move them both to keep the center.
+  if (rdx >= std::numeric_limits<int>::max() / 2) {

[Peter Mayo, 2017/03/14 18:35:59]

Maybe just on equality.

+    if (base::SaturatedAbsolute(rr) < rdx / 2)
+      rx = rr - rdx;
+    else if (base::SaturatedAbsolute(rx) > rdx / 2)
+      rx = rx + rdx / 4;
+  }
+
+  // Same computation, other axis.
+  if (rdy >= std::numeric_limits<int>::max() / 2) {
+    if (base::SaturatedAbsolute(rb) < rdy / 2)
+      ry = rb - rdy;
+    else if (base::SaturatedAbsolute(ry) > rdy / 2)
+      ry = ry + rdy / 4;
+  }
+
+  SetRect(rx, ry, rdx, rdy);
 }
 
 void Rect::Subtract(const Rect& rect) {