Revert "Revert "IWYU for tests starting with 'D'.""

This reverts commit edf8449d2c3663350b6b6e30d2fa4c70da02deef.

Change-Id: Ibeedd9965855b3ccfe44486d15307bf3da15fd9c
Reviewed-on: https://skia-review.googlesource.com/129516
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/tests/DrawTextTest.cpp b/tests/DrawTextTest.cpp
index 062d935..ac13140 100644
--- a/tests/DrawTextTest.cpp
+++ b/tests/DrawTextTest.cpp
@@ -20,7 +20,7 @@
 #include "SkTypes.h"
 #include "Test.h"
 
-#include <math.h>
+#include <cmath>
 
 static const SkColor bgColor = SK_ColorWHITE;