GrConvertPixels takes pixmaps

Add GrCPixmap, a GrPixmap but with const void* instead of void*. Share
impl via template base class GrPixmapBase.

Change-Id: I7dfdf24a73c1bc8557ff7b90f93a9399da2f3f75
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350022
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/tests/FloatingPointTextureTest.cpp b/tests/FloatingPointTextureTest.cpp
index f575bbc..c210b5b 100644
--- a/tests/FloatingPointTextureTest.cpp
+++ b/tests/FloatingPointTextureTest.cpp
@@ -50,7 +50,7 @@
 
     for (auto origin : {kTopLeft_GrSurfaceOrigin, kBottomLeft_GrSurfaceOrigin}) {
         GrImageInfo info(colorType, kPremul_SkAlphaType, nullptr, {DEV_W, DEV_H});
-        GrPixmap controlPixmap(info, controlPixelData.begin(), info.minRowBytes());
+        GrCPixmap controlPixmap(info, controlPixelData.begin(), info.minRowBytes());
         auto fpView = sk_gpu_test::MakeTextureProxyViewFromData(dContext,
                                                                 GrRenderable::kYes,
                                                                 origin,