[heap-profiler] Annotate global handles

With these annotations the corresponding global handles now have names
in DevTools, making it easy to identify where a context is held alive.

Bug: chromium:811842
Change-Id: I10df68d3024a07744e7f18a27f7c07700545a803
Reviewed-on: https://chromium-review.googlesource.com/962789Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543684}

extensions/renderer/script_context.cc

@@ -89,6 +89,7 @@ ScriptContext::ScriptContext(const v8::Local<v8::Context>& v8_context,
       safe_builtins_(this),
       isolate_(v8_context->GetIsolate()) {
   VLOG(1) << "Created context:\n" << GetDebugString();
+  v8_context_.AnnotateStrongRetainer("extensions::ScriptContext::v8_context_");
   if (web_frame_)
     url_ = GetAccessCheckedFrameURL(web_frame_);
 }

gin/context_holder.cc

@@ -21,6 +21,7 @@ ContextHolder::~ContextHolder() {
 void ContextHolder::SetContext(v8::Local<v8::Context> context) {
   DCHECK(context_.IsEmpty());
   context_.Reset(isolate_, context);
+  context_.AnnotateStrongRetainer("gin::ContextHolder::context_");
   data_.reset(new PerContextData(this, context));
 }
 

third_party/WebKit/Source/platform/bindings/ScriptState.h

@@ -175,8 +175,11 @@ class ScriptStateProtectingContext {
  public:
   ScriptStateProtectingContext(ScriptState* script_state)
       : script_state_(script_state) {
-    if (script_state_)
+    if (script_state_) {
       context_.Set(script_state_->GetIsolate(), script_state_->GetContext());
+      context_.Get().AnnotateStrongRetainer(
+          "blink::ScriptStateProtectingContext::context_");
+    }
   }
 
   ScriptState* operator->() const { return script_state_.get(); }

third_party/WebKit/Source/platform/bindings/V8PerContextData.cpp

@@ -52,6 +52,7 @@ V8PerContextData::V8PerContextData(v8::Local<v8::Context> context)
       context_(isolate_, context),
       activity_logger_(nullptr) {
   context_holder_->SetContext(context);
+  context_.Get().AnnotateStrongRetainer("blink::V8PerContextData::context_");
 
   if (IsMainThread()) {
     InstanceCounters::IncrementCounter(