Hide fields in SkImageInfo

R=rmistry@google.com
TBR=bsalomon

Author: reed@google.com

Review URL: https://codereview.chromium.org/536003002
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 9d6e856..3ac3635 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -622,11 +622,8 @@
 }
 
 void SkGradientShaderBase::GradientShaderCache::initCache32(GradientShaderCache* cache) {
-    SkImageInfo info;
-    info.fWidth = kCache32Count;
-    info.fHeight = 4;   // for our 4 dither rows
-    info.fAlphaType = kPremul_SkAlphaType;
-    info.fColorType = kN32_SkColorType;
+    const int kNumberOfDitherRows = 4;
+    const SkImageInfo info = SkImageInfo::MakeN32Premul(kCache32Count, kNumberOfDitherRows);
 
     SkASSERT(NULL == cache->fCache32PixelRef);
     cache->fCache32PixelRef = SkMallocPixelRef::NewAllocate(info, 0, NULL);