Fix overflow/underflow in gfx geometry once and for all

ui/gfx/geometry/vector2d.cc

Index: ui/gfx/geometry/vector2d.cc
diff --git a/ui/gfx/geometry/vector2d.cc b/ui/gfx/geometry/vector2d.cc
index 43f25e933a0e9c088ee298a392a6d4103a9db260..aec4d28b9b0fec0f0cdebe65f9462ac68466f4f3 100644
--- a/ui/gfx/geometry/vector2d.cc
+++ b/ui/gfx/geometry/vector2d.cc
@@ -7,6 +7,7 @@
 #include <cmath>
 
 #include "base/strings/stringprintf.h"
+#include "ui/gfx/geometry/safe_integer_conversions.h"
 
 namespace gfx {
 
@@ -15,13 +16,13 @@ bool Vector2d::IsZero() const {
 }
 
 void Vector2d::Add(const Vector2d& other) {
-  x_ += other.x_;
-  y_ += other.y_;
+  x_ = SafeAdd(other.x_, x_);
+  y_ = SafeAdd(other.y_, y_);
 }
 
 void Vector2d::Subtract(const Vector2d& other) {
-  x_ -= other.x_;
-  y_ -= other.y_;
+  x_ = SafeSubtract(x_, other.x_);
+  y_ = SafeSubtract(y_, other.y_);
 }
 
 int64_t Vector2d::LengthSquared() const {