Switch to pixmap in API.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1712653002

Review URL: https://codereview.chromium.org/1712653002
diff --git a/gm/SkLinearBitmapPipelineGM.cpp b/gm/SkLinearBitmapPipelineGM.cpp
index 7138a5d..a446b74 100644
--- a/gm/SkLinearBitmapPipelineGM.cpp
+++ b/gm/SkLinearBitmapPipelineGM.cpp
@@ -98,7 +98,6 @@
     bmdst.peekPixels(&pmdst);
 
     SkPM4f* dstBits = new SkPM4f[ir.width()];
-    SkImageInfo info = SkImageInfo::MakeN32(ir.width(), ir.height(), kPremul_SkAlphaType);
 
     SkMatrix inv;
     bool trash = mat->invert(&inv);
@@ -120,8 +119,7 @@
 
     SkLinearBitmapPipeline pipeline{
             inv, filterQuality,
-            SkShader::kClamp_TileMode, SkShader::kClamp_TileMode,
-            info, pmsrc.addr32()};
+            SkShader::kClamp_TileMode, SkShader::kClamp_TileMode, pmsrc};
 
     for (int y = 0; y < ir.height(); y++) {
         pipeline.shadeSpan4f(0, y, dstBits, ir.width());