move Sk{Test,Random}ScalerContext to tools

There's no need for Skia users to link this test code.

Change-Id: I9d6ef2a053d0cf5cb916aa254389ca819c48bae1
Reviewed-on: https://skia-review.googlesource.com/69922
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 742f095..dcecf21 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1073,6 +1073,8 @@
       "tools/LsanSuppressions.cpp",
       "tools/ProcStats.cpp",
       "tools/Resources.cpp",
+      "tools/SkRandomScalerContext.cpp",
+      "tools/SkTestScalerContext.cpp",
       "tools/ThermalManager.cpp",
       "tools/UrlDataManager.cpp",
       "tools/debugger/SkDebugCanvas.cpp",