Mark CG and WIC images as srgb

Otherwise they look funny when we draw them to srgb (drawing
untagged srcs to srgb canvas is undefined).

The image generator tests were recently changed to run on srgb.

BUG=skia:

Change-Id: I6ec07dbf736ed2a16a5db89b4028a44a98037f70
Reviewed-on: https://skia-review.googlesource.com/6182
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
diff --git a/src/ports/SkImageGeneratorCG.cpp b/src/ports/SkImageGeneratorCG.cpp
index 700a7b9..d2e6436 100644
--- a/src/ports/SkImageGeneratorCG.cpp
+++ b/src/ports/SkImageGeneratorCG.cpp
@@ -60,7 +60,7 @@
     }
 
     SkAlphaType alphaType = hasAlpha ? kPremul_SkAlphaType : kOpaque_SkAlphaType;
-    SkImageInfo info = SkImageInfo::Make(width, height, kN32_SkColorType, alphaType);
+    SkImageInfo info = SkImageInfo::MakeS32(width, height, alphaType);
 
     // FIXME: We have the opportunity to extract color space information here,
     //        though I think it makes sense to wait until we understand how