[debugger] fix break locations for assignments and return.

test/mjsunit/debug-step.js

Index: test/mjsunit/debug-step.js
diff --git a/test/mjsunit/debug-step.js b/test/mjsunit/debug-step.js
index bfbea16380cf7396c5c3571c55a0ba9f707d12ab..6f5c8f410c10d623f596fdd3e2f1bbf0513c2c16 100644
--- a/test/mjsunit/debug-step.js
+++ b/test/mjsunit/debug-step.js
@@ -64,9 +64,9 @@ function f() {
 // Set a breakpoint on the for statement (line 1).
 bp1 = Debug.setBreakPoint(f, 1);
 
-// Check that performing 1000 steps will make i 499.
+// Check that performing 1000 steps will make i 333.
 var step_count = 1000;
 result = -1;
 f();
-assertEquals(332, result);
+assertEquals(333, result);
 Debug.setListener(null);