inspector: teach v8Inspector to return default context

This is a follow-up to https://chromium-review.googlesource.com/c/v8/v8/+/1173718

R=kozy, pfeldman
TBR=pfeldman

Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;luci.chromium.try:linux_chromium_rel_ng;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I48b4ca5589505d03773477623654fa54703f0714
Reviewed-on: https://chromium-review.googlesource.com/1175061
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55133}

include/v8-inspector.h

@@ -245,7 +245,8 @@ class V8_EXPORT V8Inspector {
   virtual void contextCreated(const V8ContextInfo&) = 0;
   virtual void contextDestroyed(v8::Local<v8::Context>) = 0;
   virtual void resetContextGroup(int contextGroupId) = 0;
-  virtual v8::MaybeLocal<v8::Context> contextById(int contextId) = 0;
+  virtual v8::MaybeLocal<v8::Context> contextById(int groupId,
+                                                  v8::Maybe<int> contextId) = 0;
 
   // Various instrumentation.
   virtual void idleStarted() = 0;

src/inspector/v8-inspector-impl.cc

@@ -188,8 +188,14 @@ InspectedContext* V8InspectorImpl::getContext(int contextId) const {
   return getContext(contextGroupId(contextId), contextId);
 }
 
-v8::MaybeLocal<v8::Context> V8InspectorImpl::contextById(int contextId) {
-  InspectedContext* context = getContext(contextId);
+v8::MaybeLocal<v8::Context> V8InspectorImpl::contextById(
+    int groupId, v8::Maybe<int> contextId) {
+  if (contextId.IsNothing()) {
+    v8::Local<v8::Context> context =
+        client()->ensureDefaultContextInGroup(groupId);
+    return context.IsEmpty() ? v8::MaybeLocal<v8::Context>() : context;
+  }
+  InspectedContext* context = getContext(contextId.FromJust());
   return context ? context->context() : v8::MaybeLocal<v8::Context>();
 }
 

src/inspector/v8-inspector-impl.h

@@ -78,7 +78,8 @@ class V8InspectorImpl : public V8Inspector {
                                               const StringView& state) override;
   void contextCreated(const V8ContextInfo&) override;
   void contextDestroyed(v8::Local<v8::Context>) override;
-  v8::MaybeLocal<v8::Context> contextById(int contextId) override;
+  v8::MaybeLocal<v8::Context> contextById(int groupId,
+                                          v8::Maybe<int> contextId) override;
   void contextCollected(int contextGroupId, int contextId);
   void resetContextGroup(int contextGroupId) override;
   void idleStarted() override;