Add mipmap support to SkPixmap flavor of createBackendTexture

Change-Id: I7a2dea9b0b8e6b985f2d56e587939266022c19e1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234664
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/tests/MtlBackendAllocationTest.mm b/tests/MtlBackendAllocationTest.mm
index a9384cb..d3bfc79 100644
--- a/tests/MtlBackendAllocationTest.mm
+++ b/tests/MtlBackendAllocationTest.mm
@@ -32,10 +32,11 @@
     const GrMtlCaps* mtlCaps = static_cast<const GrMtlCaps*>(context->priv().caps());
 
     constexpr SkColor4f kTransCol { 0, 0.25f, 0.75f, 0.5f };
+    constexpr SkColor4f kGrayCol { 0.75f, 0.75f, 0.75f, 0.75f };
 
     struct {
         GrColorType      fColorType;
-        MTLPixelFormat fFormat;
+        MTLPixelFormat   fFormat;
         SkColor4f        fColor;
     } combinations[] = {
         { GrColorType::kRGBA_8888,        MTLPixelFormatRGBA8Unorm,      SkColors::kRed       },
@@ -56,7 +57,7 @@
 
         { GrColorType::kAlpha_8,          MTLPixelFormatA8Unorm,         kTransCol            },
         { GrColorType::kAlpha_8,          MTLPixelFormatR8Unorm,         kTransCol            },
-        { GrColorType::kGray_8,           MTLPixelFormatR8Unorm,         SkColors::kDkGray    },
+        { GrColorType::kGray_8,           MTLPixelFormatR8Unorm,         kGrayCol             },
 
         { GrColorType::kRGBA_F32,         MTLPixelFormatRGBA32Float,     SkColors::kRed       },
 
@@ -114,7 +115,6 @@
                                   combo.fColorType, mipMapped, renderable);
                 }
 
-                // Not implemented for Metal yet
                 {
                     auto createWithColorMtd = [format](GrContext* context,
                                                        const SkColor4f& color,