Implement Sk2f::floor

Bug: skia:
Change-Id: Id40e7165a338d321df71a1852b48eb2570ecd75b
Reviewed-on: https://skia-review.googlesource.com/133460
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/tests/SkNxTest.cpp b/tests/SkNxTest.cpp
index 933a5fc..a454043 100644
--- a/tests/SkNxTest.cpp
+++ b/tests/SkNxTest.cpp
@@ -257,6 +257,14 @@
     REPORTER_ASSERT(r, fs[1] == -1.0f);
     REPORTER_ASSERT(r, fs[2] ==  0.0f);
     REPORTER_ASSERT(r, fs[3] == -1.0f);
+
+    auto fs2 = Sk2f(0.4f, -0.4f).floor();
+    REPORTER_ASSERT(r, fs2[0] ==  0.0f);
+    REPORTER_ASSERT(r, fs2[1] == -1.0f);
+
+    auto fs3 = Sk2f(0.6f, -0.6f).floor();
+    REPORTER_ASSERT(r, fs3[0] ==  0.0f);
+    REPORTER_ASSERT(r, fs3[1] == -1.0f);
 }
 
 DEF_TEST(SkNx_shuffle, r) {