move a bunch of helpers from SkImageInfo.h into priv

Bug: skia:
Change-Id: I8c91cfdb89e4f22448d1201d391556fe43d86dca
Reviewed-on: https://skia-review.googlesource.com/105289
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Cary Clark <caryclark@google.com>
diff --git a/tests/ImageGeneratorTest.cpp b/tests/ImageGeneratorTest.cpp
index 7ee0b90..8a7f0de 100644
--- a/tests/ImageGeneratorTest.cpp
+++ b/tests/ImageGeneratorTest.cpp
@@ -9,6 +9,7 @@
 #include "SkCanvas.h"
 #include "SkGraphics.h"
 #include "SkImageGenerator.h"
+#include "SkImageInfoPriv.h"
 #include "Test.h"
 
 static bool gMyFactoryWasCalled;