Fix AngleBetweenVectorsInDegrees NAN

Fixes potential NANs from gfx::AngleBetweenVectorsInDegrees and
gfx::ClockwiseAngleBetweenVectorsInDegrees when the given vectors are
very close together by clamping the value passed to acos. When
unclamped, the value passed to acos could be slightly outside [-1, 1]
due to floating point precision.

Bug: 918734
Change-Id: I55b75b21581d25134fdc3e8e6db80892607a807c
Reviewed-on: https://chromium-review.googlesource.com/c/1394086Reviewed-by: Ian Vollick <vollick@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619780}

ui/gfx/geometry/vector3d_f.cc

@@ -86,8 +86,11 @@ Vector3dF ScaleVector3d(const Vector3dF& v,
 
 float AngleBetweenVectorsInDegrees(const gfx::Vector3dF& base,
                                    const gfx::Vector3dF& other) {
-  return gfx::RadToDeg(
-      std::acos(gfx::DotProduct(base, other) / base.Length() / other.Length()));
+  // Clamp the resulting value to prevent potential NANs from floating point
+  // precision issues.
+  return gfx::RadToDeg(std::acos(fmax(
+      fmin(gfx::DotProduct(base, other) / base.Length() / other.Length(), 1.f),
+      -1.f)));
 }
 
 float ClockwiseAngleBetweenVectorsInDegrees(const gfx::Vector3dF& base,

ui/gfx/geometry/vector3d_unittest.cc

@@ -270,14 +270,16 @@ TEST(Vector3dTest, AngleBetweenVectorsInDegress) {
     float expected;
     gfx::Vector3dF input1;
     gfx::Vector3dF input2;
-  } tests[] = {
-      {0, gfx::Vector3dF(0, 1, 0), gfx::Vector3dF(0, 1, 0)},
-      {90, gfx::Vector3dF(0, 1, 0), gfx::Vector3dF(0, 0, 1)},
-      {45,
-       gfx::Vector3dF(0, 1, 0),
-       gfx::Vector3dF(0, 0.70710678188f, 0.70710678188f)},
-      {180, gfx::Vector3dF(0, 1, 0), gfx::Vector3dF(0, -1, 0)},
-  };
+  } tests[] = {{0, gfx::Vector3dF(0, 1, 0), gfx::Vector3dF(0, 1, 0)},
+               {90, gfx::Vector3dF(0, 1, 0), gfx::Vector3dF(0, 0, 1)},
+               {45, gfx::Vector3dF(0, 1, 0),
+                gfx::Vector3dF(0, 0.70710678188f, 0.70710678188f)},
+               {180, gfx::Vector3dF(0, 1, 0), gfx::Vector3dF(0, -1, 0)},
+               // Two vectors that are sufficiently close enough together to
+               // trigger an issue that produces NANs if the value passed to
+               // acos is not clamped due to floating point precision.
+               {0, gfx::Vector3dF(0, -0.990842f, -0.003177f),
+                gfx::Vector3dF(0, -0.999995f, -0.003124f)}};
 
   for (size_t i = 0; i < base::size(tests); ++i) {
     float actual =