Change interface block's fVariable from ref to pointer

The next pre-include refactor will require cloning InterfaceBlocks, and
re-targeting the variable.

Change-Id: Iccfc1f39789fcd572199682386cd612500334061
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/323890
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
diff --git a/src/sksl/SkSLDehydrator.cpp b/src/sksl/SkSLDehydrator.cpp
index 2b81eaa..22071cc 100644
--- a/src/sksl/SkSLDehydrator.cpp
+++ b/src/sksl/SkSLDehydrator.cpp
@@ -545,7 +545,7 @@
         case ProgramElement::Kind::kInterfaceBlock: {
             const InterfaceBlock& i = e.as<InterfaceBlock>();
             this->writeU8(Rehydrator::kInterfaceBlock_Command);
-            this->write(i.fVariable);
+            this->write(*i.fVariable);
             this->write(i.fTypeName);
             this->write(i.fInstanceName);
             this->writeU8(i.fSizes.size());