[instrumentation] Generalize instrumentation to be used beyond the core layer

third_party/WebKit/Source/platform/loader/fetch/FetchContext.h

Index: third_party/WebKit/Source/platform/loader/fetch/FetchContext.h
diff --git a/third_party/WebKit/Source/platform/loader/fetch/FetchContext.h b/third_party/WebKit/Source/platform/loader/fetch/FetchContext.h
index e2061029aff5b89e6d90a9143787ff2db8832467..30ddd9010eb66003ed7b575c3e6cd86948e3fe72 100644
--- a/third_party/WebKit/Source/platform/loader/fetch/FetchContext.h
+++ b/third_party/WebKit/Source/platform/loader/fetch/FetchContext.h
@@ -48,6 +48,7 @@ namespace blink {
 class ClientHintsPreferences;
 class KURL;
 class MHTMLArchive;
+class PlatformInstrumentationAgents;
 class ResourceError;
 class ResourceResponse;
 class ResourceTimingInfo;
@@ -73,7 +74,8 @@ class PLATFORM_EXPORT FetchContext
   static FetchContext& nullInstance();
 
   virtual ~FetchContext() {}
-  DEFINE_INLINE_VIRTUAL_TRACE() {}
+
+  DECLARE_VIRTUAL_TRACE();
 
   virtual bool isLiveContext() { return false; }
 
@@ -188,8 +190,15 @@ class PLATFORM_EXPORT FetchContext
 
   virtual RefPtr<WebTaskRunner> loadingTaskRunner() const { return nullptr; }
 
+  PlatformInstrumentationAgents* instrumentingAgents() const {
+    return m_instrumentingAgents;
+  }
+
  protected:
-  FetchContext() {}
+  FetchContext();
+
+ private:
+  Member<PlatformInstrumentationAgents> m_instrumentingAgents;
 };
 
 }  // namespace blink