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

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

Index: third_party/WebKit/Source/platform/loader/fetch/FetchContext.cpp
diff --git a/third_party/WebKit/Source/platform/loader/fetch/FetchContext.cpp b/third_party/WebKit/Source/platform/loader/fetch/FetchContext.cpp
index 00b0a35a54711fa117d8636445f00d4ab1e17bd1..26cbe117e58ef2f95ad981fa80378720dc6eb1b4 100644
--- a/third_party/WebKit/Source/platform/loader/fetch/FetchContext.cpp
+++ b/third_party/WebKit/Source/platform/loader/fetch/FetchContext.cpp
@@ -30,6 +30,8 @@
 
 #include "platform/loader/fetch/FetchContext.h"
 
+#include "platform/PlatformInstrumentationAgents.h"
+#include "platform/instrumentation/PlatformTraceEventsAgent.h"
 #include "public/platform/WebCachePolicy.h"
 
 namespace blink {
@@ -39,6 +41,16 @@ FetchContext& FetchContext::nullInstance() {
   return instance;
 }
 
+FetchContext::FetchContext()
+    : m_instrumentingAgents(new PlatformInstrumentationAgents) {
+  m_instrumentingAgents->addPlatformTraceEventsAgent(
+      new PlatformTraceEventsAgent);
+}
+
+DEFINE_TRACE(FetchContext) {
+  visitor->trace(m_instrumentingAgents);
+}
+
 void FetchContext::dispatchDidChangeResourcePriority(unsigned long,
                                                      ResourceLoadPriority,
                                                      int) {}