Clean up EGL thread state at thread exit in nanobench and DM

src/core/SkTaskGroup.h

Index: src/core/SkTaskGroup.h
diff --git a/src/core/SkTaskGroup.h b/src/core/SkTaskGroup.h
index 0d86cdb82934fefa17274c4a99e714f7751aa8b0..ce9a7b2b3326035ab67602cf7f5e7c08326073ef 100644
--- a/src/core/SkTaskGroup.h
+++ b/src/core/SkTaskGroup.h
@@ -18,8 +18,13 @@ class SkTaskGroup : SkNoncopyable {
 public:
     // Create one of these in main() to enable SkTaskGroups globally.
     struct Enabler : SkNoncopyable {
-        explicit Enabler(int threads = -1);  // Default is system-reported core count.
+        // @param threads Default is system-reported core count.
+        // @param cleanupFn Function to call in each thread that may have
+        //        scheduled SkTaskGroup tasks.
+        explicit Enabler(int threads = -1, std::function<void(void)> cleanupFn = nullptr);
         ~Enabler();
+      private:
+        std::function<void(void)> fCleanupFn;
     };
 
     SkTaskGroup();