[vm,debugger] Do not stop at hoisted variable declarations when stepping through patterns

TEST=pkg/vm_service/test/step_through_patterns_test.dart
Issue: #51812
Issue: #49755

Change-Id: Ieb2e6f49c613c7543e7e76119cefbc4d8f9ae3de
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/291840
Commit-Queue: Alexander Markov <[email protected]>
Reviewed-by: Ben Konyi <[email protected]>

Author: alexmarkov

pkg/vm_service/test/step_through_patterns_test.dart

@@ -43,15 +43,11 @@ List<String> expected = [
   "$FILE:${LINE + 0}:46", // on 'shape' after 'switch'
   "$FILE:${LINE + 1}:20", // on ':'
   "$FILE:${LINE + 2}:20", // on ':'
-  "$FILE:${LINE + 1}:26", // on 'l' right after 'var'
   "$FILE:${LINE + 1}:7", // on 'Square'
-  "$FILE:${LINE + 2}:26", // on 'r' right after 'var'
   "$FILE:${LINE + 2}:7", // on 'Circle'
   "$FILE:${LINE + 2}:26", // on 'r' right after 'var'
   "$FILE:${LINE + 2}:36", // on '>='
-  "$FILE:${LINE + 3}:26", // on 'l' right after 'var'
   "$FILE:${LINE + 1}:7", // on 'Square'
-  "$FILE:${LINE + 4}:26", // on 'r' right after 'var'
   "$FILE:${LINE + 2}:7", // on 'Circle'
   "$FILE:${LINE + 4}:26", // on 'r' right after 'var'
   "$FILE:${LINE + 4}:36", // on '<'

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -5802,7 +5802,7 @@ Fragment StreamingFlowGraphBuilder::BuildVariableDeclaration(
                                            ? helper.equals_position_
                                            : helper.position_;
   if (position != nullptr) *position = helper.position_;
-  if (NeedsDebugStepCheck(stack(), debug_position)) {
+  if (NeedsDebugStepCheck(stack(), debug_position) && !helper.IsHoisted()) {
     instructions = DebugStepCheck(debug_position) + instructions;
   }
   instructions += StoreLocal(helper.position_, variable);