Add Vector2d classes that represent offsets, instead of using Point.

ui/gfx/point_unittest.cc

Index: ui/gfx/point_unittest.cc
diff --git a/ui/gfx/point_unittest.cc b/ui/gfx/point_unittest.cc
index cae21660f31481d2fe9cd8a59a180fb70575c109..ea42b53f1faa03b4468776e65199da19ff5203a0 100644
--- a/ui/gfx/point_unittest.cc
+++ b/ui/gfx/point_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "ui/gfx/point_base.h"
 
+#include "base/basictypes.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/point_f.h"
@@ -47,4 +48,36 @@ TEST(PointTest, IsOrigin) {
   EXPECT_TRUE(gfx::PointF(0, 0).IsOrigin());
 }
 
+TEST(PointTest, VectorArithmetic) {
+  gfx::Point a(1, 5);
+  gfx::Vector2d v1(3, -3);
+  gfx::Vector2d v2(-8, 1);
+
+  static const struct {
+    gfx::Point expected;
+    gfx::Point actual;
+  } tests[] = {
+    { gfx::Point(4, 2), a + v1 },
+    { gfx::Point(-2, 8), a - v1 },
+    { a, a - v1 + v1 },
+    { a, a + v1 - v1 },
+    { a, a + gfx::Vector2d() },
+    { gfx::Point(12, 1), a + v1 - v2 },
+    { gfx::Point(-10, 9), a - v1 + v2 }
+  };
+
+  for (size_t i = 0; i < ARRAYSIZE_UNSAFE(tests); ++i)
+    EXPECT_EQ(tests[i].expected.ToString(),
+              tests[i].actual.ToString());
+}
+
+TEST(PointTest, OffsetFromPoint) {
+  gfx::Point a(1, 5);
+  gfx::Point b(-20, 8);
+  EXPECT_EQ(gfx::Vector2d(-20 - 1, 8 - 5).ToString(),
+            b.OffsetFrom(a).ToString());
+  EXPECT_EQ(gfx::Vector2d(-20 - 1, 8 - 5).ToString(),
+            (b - a).ToString());
+}
+
 }  // namespace ui