Migrate ModifiersPool into the context.

The IRGenerator no longer owns the pool of modifiers; they are now
available to any function that has a Context.

Change-Id: I4f2f37ae5e06966bed00107b0483b42b07a454d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/404237
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/dsl/priv/DSLWriter.h b/src/sksl/dsl/priv/DSLWriter.h
index cc5d7a8..e7e96b8 100644
--- a/src/sksl/dsl/priv/DSLWriter.h
+++ b/src/sksl/dsl/priv/DSLWriter.h
@@ -214,9 +214,11 @@
 
 private:
     std::unique_ptr<SkSL::ProgramConfig> fConfig;
+    std::unique_ptr<SkSL::ModifiersPool> fModifiersPool;
     SkSL::Compiler* fCompiler;
     std::unique_ptr<Pool> fPool;
     SkSL::ProgramConfig* fOldConfig;
+    SkSL::ModifiersPool* fOldModifiersPool;
     std::vector<std::unique_ptr<SkSL::ProgramElement>> fProgramElements;
     std::vector<const SkSL::ProgramElement*> fSharedElements;
     ErrorHandler* fErrorHandler = nullptr;