Remove SkPM4fPriv.h includes, then IWYU

Bug: skia:
Change-Id: Ie59aace6ba7ca3685d481fcb3af508629c56f0c3
Reviewed-on: https://skia-review.googlesource.com/157742
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/gradients/GrGradientBitmapCache.cpp b/src/gpu/gradients/GrGradientBitmapCache.cpp
index dd4e842..9caa081 100644
--- a/src/gpu/gradients/GrGradientBitmapCache.cpp
+++ b/src/gpu/gradients/GrGradientBitmapCache.cpp
@@ -11,7 +11,7 @@
 #include "SkMalloc.h"
 #include "SkFloatBits.h"
 #include "SkHalf.h"
-#include "SkPM4fPriv.h"
+#include "SkPM4f.h"
 #include "SkTemplates.h"
 
 #include <functional>