Add a Slug bot

Add a Mac Mini to test using GrSlug drawing instead of using
GrTextBlob for drawing.

Change-Id: I28ee402b7f82ae235518ee585d5803857490f8e1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/535964
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Herb Derby <herb@google.com>

infra/bots/gen_tasks_logic/dm_flags.go

@@ -453,6 +453,10 @@ func (b *taskBuilder) dmFlags(internalHardwareLabel string) {
 				configs = append(configs, "mtlmsaa4")
 			}
 		}
+		if b.extraConfig("Slug") {
+		    // Test slug drawing
+		    configs = []string{"glslug"}
+		}
 		if b.extraConfig("Direct3D") {
 			configs = []string{"d3d"}
 		}

infra/bots/jobs.json

@@ -102,6 +102,7 @@
   {"name": "Build-Mac-Clang-arm64-Debug"},
   {"name": "Build-Mac-Clang-arm64-Debug-Android"},
   {"name": "Build-Mac-Clang-arm64-Debug-Metal"},
+  {"name": "Build-Mac-Clang-arm64-Debug-Slug"},
   {"name": "Build-Mac-Clang-arm64-Debug-iOS"},
   {"name": "Build-Mac-Clang-arm64-Debug-iOS_Metal"},
   {"name": "Build-Mac-Xcode11.4.1-arm64-Debug-iOS_Metal"},
@@ -617,6 +618,7 @@
   {"name": "Test-Mac12-Clang-MacMini9.1-CPU-AppleM1-arm64-Debug-All-NativeFonts_ASAN"},
   {"name": "Test-Mac12-Clang-MacMini9.1-GPU-AppleM1-arm64-Debug-All-NativeFonts"},
   {"name": "Test-Mac12-Clang-MacMini9.1-GPU-AppleM1-arm64-Debug-All-Metal"},
+  {"name": "Test-Mac12-Clang-MacMini9.1-GPU-AppleM1-arm64-Debug-All-Slug"},
   {"name": "Test-Mac12-Clang-MacMini9.1-GPU-AppleM1-arm64-Release-All-Metal"},
   {"name": "Test-Ubuntu18-Clang-Golo-GPU-QuadroP400-x86_64-Debug-All-DDL1"},
   {"name": "Test-Ubuntu18-Clang-Golo-GPU-QuadroP400-x86_64-Debug-All-DDL1_Vulkan"},