Added fastbuild config variable to isolate.gypi to let isolates test it.

chrome/telemetry_gpu_test.isolate

 # Copyright (c) 2013 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.
 {
   'includes': [
     'telemetry.isolate',
   ],
   'conditions': [
     ['OS=="android" or OS=="linux" or OS=="mac" or OS=="win"', {
       # This isolate allows any of the GPU tests, including the WebGL
       # conformance tests, to be run. However, extra command line arguments
       # must be supplied in order to run any one of them.
       'variables': {
         'isolate_dependency_untracked': [
           '../content/test/gpu/',
           '../content/test/data/gpu/',
           # For GpuProcess.video
           '../content/test/data/media/bear.ogv',
           # For webgl_conformance
           '../third_party/webgl/',
         ],
         'command': [
           '../content/test/gpu/run_gpu_test.py',
         ],
       },
     }],
+    # For debugging crbug.com/383963
+    ['OS=="win" and (fastbuild==0 or fastbuild==1)', {
+      'variables': {
+        'isolate_dependency_tracked': [
+          '<(PRODUCT_DIR)/chrome_child.dll.pdb',
+        ],
+      },
+    }],
   ]
 }