Expose compatibility layer stack frame on thread

For #212

src/compiler/compat-block-utility.js

@@ -3,12 +3,11 @@ const BlockUtility = require('../engine/block-utility');
 class CompatibilityLayerBlockUtility extends BlockUtility {
     constructor () {
         super();
-        this._stackFrame = {};
         this._startedBranch = null;
     }
 
     get stackFrame () {
-        return this._stackFrame;
+        return this.thread.compatibilityStackFrame;
     }
 
     startBranch (branchNumber, isLoop) {
@@ -33,9 +32,9 @@ class CompatibilityLayerBlockUtility extends BlockUtility {
     init (thread, fakeBlockId, stackFrame) {
         this.thread = thread;
         this.sequencer = thread.target.runtime.sequencer;
-        this._stackFrame = stackFrame;
         this._startedBranch = null;
         thread.stack[0] = fakeBlockId;
+        thread.compatibilityStackFrame = stackFrame;
     }
 }
 

src/engine/thread.js

@@ -215,6 +215,7 @@ class Thread {
          */
         this.procedures = null;
         this.executableHat = false;
+        this.compatibilityStackFrame = null;
     }
 
     /**

test/integration/tw_compat_block_utility_stackframe_exposed.js

@@ -0,0 +1,15 @@
+const {test} = require('tap');
+const fs = require('fs');
+const path = require('path');
+const VM = require('../../src/virtual-machine');
+const Timer = require('../../src/util/timer');
+
+test('compatibility stack frame is exposed on thread', t => {
+    const vm = new VM();
+    vm.loadProject(fs.readFileSync(path.join(__dirname, '../fixtures/tw-glide.sb3'))).then(() => {
+        vm.greenFlag();
+        vm.runtime._step();
+        t.ok(vm.runtime.threads[0].compatibilityStackFrame.timer instanceof Timer);
+        t.end();
+    });
+});