Add REPORTF test macro.

tests/MathTest.cpp

Index: tests/MathTest.cpp
diff --git a/tests/MathTest.cpp b/tests/MathTest.cpp
index 8cba67dd3d49528db789aceecdf0fca05e0995bc..2756dc428c78442c888cefc30025857169d9efe4 100644
--- a/tests/MathTest.cpp
+++ b/tests/MathTest.cpp
@@ -225,10 +225,9 @@ static bool equal_float_native_skia(float x, uint32_t ni, uint32_t si) {
 static void assert_float_equal(skiatest::Reporter* reporter, const char op[],
                                float x, uint32_t ni, uint32_t si) {
     if (!equal_float_native_skia(x, ni, si)) {
-        SkString desc;
-        uint32_t xi = SkFloat2Bits(x);
-        desc.printf("%s float %g bits %x native %x skia %x\n", op, x, xi, ni, si);
-        reporter->reportFailed(desc);
+        REPORTF(reporter,
+                ("%s float %g bits %x native %x skia %x\n",
+                 op, x, SkFloat2Bits(x), ni, si));
     }
 }