Reduced skslc memory consumption

src/sksl/ir/SkSLType.h

Index: src/sksl/ir/SkSLType.h
diff --git a/src/sksl/ir/SkSLType.h b/src/sksl/ir/SkSLType.h
index ad2185b4ee183ac82fc7af2bf4ea2facbe17250a..afd00d8b2af41d9a54c7b61047558dcb871d34f8 100644
--- a/src/sksl/ir/SkSLType.h
+++ b/src/sksl/ir/SkSLType.h
@@ -57,7 +57,9 @@ public:
     : INHERITED(Position(), kType_Kind, std::move(name))
     , fTypeKind(kOther_Kind) {}
 
-    // Create a generic type which maps to the listed types.
+    // Create a generic type which maps to the listed types. As currently implemented, there are 
+    // always exactly four coercion targets, mapping to the scalar, vec2, vec3, and vec4 versions of 
+    // a type.
     Type(std::string name, std::vector<const Type*> types)
     : INHERITED(Position(), kType_Kind, std::move(name))
     , fTypeKind(kGeneric_Kind)