[V8] Add FunctionMirror.prototype.contextDebugId method

This method returns contextDebugId for function. We can't use context_data from FunctionMirror.prototype.script because it can be incorrect when compilation cache is used and one script object was used for JSFunctions in different contexts.

BUG=chromium:595206
LOG=Y
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1840713002

Cr-Commit-Position: refs/heads/master@{#35117}

src/debug/mirrors.js

@@ -1037,6 +1037,15 @@ FunctionMirror.prototype.toText = function() {
 };
 
 
+FunctionMirror.prototype.context = function() {
+  if (this.resolved()) {
+    if (!this._context)
+      this._context = new ContextMirror(%FunctionGetContextData(this.value_));
+    return this._context;
+  }
+};
+
+
 /**
  * Mirror object for unresolved functions.
  * @param {string} value The name for the unresolved function reflected by this

src/runtime/runtime-function.cc

@@ -96,6 +96,14 @@ RUNTIME_FUNCTION(Runtime_FunctionGetPositionForOffset) {
   return Smi::FromInt(abstract_code->SourcePosition(offset));
 }
 
+RUNTIME_FUNCTION(Runtime_FunctionGetContextData) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 1);
+
+  CONVERT_ARG_CHECKED(JSFunction, fun, 0);
+  FixedArray* array = fun->native_context()->embedder_data();
+  return array->get(v8::Context::kDebugIdIndex);
+}
 
 RUNTIME_FUNCTION(Runtime_FunctionSetInstanceClassName) {
   SealHandleScope shs(isolate);

src/runtime/runtime.h

@@ -218,6 +218,7 @@ namespace internal {
   F(FunctionGetSourceCode, 1, 1)           \
   F(FunctionGetScriptSourcePosition, 1, 1) \
   F(FunctionGetPositionForOffset, 2, 1)    \
+  F(FunctionGetContextData, 1, 1)          \
   F(FunctionSetInstanceClassName, 2, 1)    \
   F(FunctionSetLength, 2, 1)               \
   F(FunctionSetPrototype, 2, 1)            \