[debugger] infrastructure for side-effect-free debug-evaluate.

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index 281ba29695d54ebd8d26aba7376706641180dbc9..5b9ebe537af2d35bd7e3230e34e3bf2851f09d27 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -5,6 +5,7 @@
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
+#include "src/compiler.h"
 #include "src/debug/debug-evaluate.h"
 #include "src/debug/debug-frames.h"
 #include "src/debug/debug-scopes.h"
@@ -1857,6 +1858,21 @@ RUNTIME_FUNCTION(Runtime_DebugPrepareStepInIfStepping) {
   return isolate->heap()->undefined_value();
 }
 
+// Perform %DebugPrepareStepInIfStepping and a read-only check.
+RUNTIME_FUNCTION(Runtime_DebugOnFunctionCall) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);
+  if (isolate->debug()->last_step_action() >= StepIn) {

[jgruber, 2017/01/10 12:46:38]

Maybe we should refactor these '>= StepIn' checks to improve readability and
robustness (e.g. what if we add a new step action). It's also not documented in
debug.h that the order of StepActions is significant. 

[Yang, 2017/01/10 14:14:07]

We do have static asserts in many places to guard the order. I'd like to do that
clean up in a separate CL.

+    isolate->debug()->PrepareStepIn(fun);
+  }
+  if (isolate->debug()->needs_readonly_check() &&
+      !isolate->debug()->PerformReadOnlyCheck(fun)) {
+    return isolate->heap()->exception();
+  }
+  return isolate->heap()->undefined_value();
+}
+
 // Set one shot breakpoints for the suspended generator object.
 RUNTIME_FUNCTION(Runtime_DebugPrepareStepInSuspendedGenerator) {
   HandleScope scope(isolate);