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

third_party/WebKit/Source/platform/instrumentation/PlatformInstrumentation.idl

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+interface PlatformInstrumentation {
+
+#define PROBE_EXPORT PLATFORM_EXPORT
+
+class FetchContext;
+class ResourceRequest;
+class ResourceResponse;
+struct FetchInitiatorInfo;
+
+    [PlatformTraceEvents]
+    PlatformSendRequest([Keep] FetchContext*, unsigned long identifier, ResourceRequest&, const ResourceResponse& redirectResponse, const FetchInitiatorInfo&);
+}