Undo issue 14983004 to conform to spec.

This change reverts the change in issue 14983004 (gfx::BlendDecomposedTransforms
should interpolate rotations along the shortest path). Although it may be
desirable for the interpolation to occur along the shortest path (as discussed
in http://lists.w3.org/Archives/Public/www-style/2013May/0131.html), the spec
has not been changed. So this patch brings ui/gfx back in line with the spec.

BUG=

Review URL: https://codereview.chromium.org/1039993003

Cr-Commit-Position: refs/heads/master@{#324816}

2 files changed, 1 insertions, 57 deletions

diff --git a/ui/gfx/transform_unittest.cc b/ui/gfx/transform_unittest.cc
index 7d4d8ad..1944142 100644
--- a/ui/gfx/transform_unittest.cc
+++ b/ui/gfx/transform_unittest.cc
@@ -735,49 +735,6 @@ TEST(XFormTest, BlendRotate) {
   }
 }
 
-#if defined(_WIN64)
-// http://crbug.com/406574
-#define MAYBE_BlendRotateFollowsShortestPath DISABLED_BlendRotateFollowsShortestPath
-#else
-#define MAYBE_BlendRotateFollowsShortestPath BlendRotateFollowsShortestPath
-#endif
-TEST(XFormTest, MAYBE_BlendRotateFollowsShortestPath) {
-  // Verify that we interpolate along the shortest path regardless of whether
-  // this path crosses the 180-degree point.
-  Vector3dF axes[] = {
-    Vector3dF(1, 0, 0),
-    Vector3dF(0, 1, 0),
-    Vector3dF(0, 0, 1),
-    Vector3dF(1, 1, 1)
-  };
-  for (size_t index = 0; index < arraysize(axes); ++index) {
-    for (int i = -5; i < 15; ++i) {
-      Transform from1;
-      from1.RotateAbout(axes[index], 130.0);
-      Transform to1;
-      to1.RotateAbout(axes[index], 175.0);
-
-      Transform from2;
-      from2.RotateAbout(axes[index], 140.0);
-      Transform to2;
-      to2.RotateAbout(axes[index], 185.0);
-
-      double t = i / 9.0;
-      EXPECT_TRUE(to1.Blend(from1, t));
-      EXPECT_TRUE(to2.Blend(from2, t));
-
-      Transform expected1;
-      expected1.RotateAbout(axes[index], 130.0 + 45.0 * t);
-
-      Transform expected2;
-      expected2.RotateAbout(axes[index], 140.0 + 45.0 * t);
-
-      EXPECT_TRUE(MatricesAreNearlyEqual(expected1, to1));
-      EXPECT_TRUE(MatricesAreNearlyEqual(expected2, to2));
-    }
-  }
-}
-
 TEST(XFormTest, CanBlend180DegreeRotation) {
   Vector3dF axes[] = {
     Vector3dF(1, 0, 0),
diff --git a/ui/gfx/transform_util.cc b/ui/gfx/transform_util.cc
index 5c9fb50..3eab6e2 100644
--- a/ui/gfx/transform_util.cc
+++ b/ui/gfx/transform_util.cc
@@ -66,19 +66,6 @@ bool Slerp(SkMScalar out[4],
   // Clamp product to -1.0 <= product <= 1.0.
   product = std::min(std::max(product, -1.0), 1.0);
 
-  // Interpolate angles along the shortest path. For example, to interpolate
-  // between a 175 degree angle and a 185 degree angle, interpolate along the
-  // 10 degree path from 175 to 185, rather than along the 350 degree path in
-  // the opposite direction. This matches WebKit's implementation but not
-  // the current W3C spec. Fixing the spec to match this approach is discussed
-  // at:
-  // http://lists.w3.org/Archives/Public/www-style/2013May/0131.html
-  double scale1 = 1.0;
-  if (product < 0) {
-    product = -product;
-    scale1 = -1.0;
-  }
-
   const double epsilon = 1e-5;
   if (std::abs(product - 1.0) < epsilon) {
     for (int i = 0; i < 4; ++i)
@@ -90,7 +77,7 @@ bool Slerp(SkMScalar out[4],
   double theta = std::acos(product);
   double w = std::sin(progress * theta) * (1.0 / denom);
 
-  scale1 *= std::cos(progress * theta) - product * w;
+  double scale1 = std::cos(progress * theta) - product * w;
   double scale2 = w;
   Combine<4>(out, q1, q2, scale1, scale2);