Reland "SkSL is now pickier about type conversions"

This is a reland of 91c1d08bc391c997418512b9599f3acd3b2c985d

Original change's description:
> SkSL is now pickier about type conversions
> 
> Bug: skia:
> Change-Id: I4e8b8f229f4e4344f160b0dbb41832764d0b75bd
> Reviewed-on: https://skia-review.googlesource.com/c/188311
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

Bug: skia:
Change-Id: I727cad061afc0a5ee6f4d2df789330d809dd110a
Reviewed-on: https://skia-review.googlesource.com/c/189643
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/gpu/vk/GrVkUtil.cpp b/src/gpu/vk/GrVkUtil.cpp
index a86804b..8dffe4c 100644
--- a/src/gpu/vk/GrVkUtil.cpp
+++ b/src/gpu/vk/GrVkUtil.cpp
@@ -204,6 +204,7 @@
                                                               SkSL::String(shaderString),
                                                               settings);
     if (!program) {
+        printf("%s\n", shaderString);
         SkDebugf("SkSL error:\n%s\n", gpu->shaderCompiler()->errorText().c_str());
         SkASSERT(false);
     }