Add dbghelp.dll that works on XP, and include in base.isolate

base/base.isolate

 # Copyright 2014 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': [
     # While the target 'base' doesn't depend on ../third_party/icu/icu.gyp
     # itself, virtually all targets using it has to include icu. The only
     # exception is the Windows sandbox (?).
     '../third_party/icu/icu.isolate',
   ],
@@ skipping 12 matching lines @@
         ],
       },
     }],
     ['OS=="mac" and asan==1', {
       'variables': {
         'files': [
           '<(PRODUCT_DIR)/libclang_rt.asan_osx_dynamic.dylib',
         ],
       },
     }],
+    ['OS=="win"', {
+      # Required for base/stack_trace_win.cc to symbolize correctly.
+      'variables': {
+        'files': [
+          '../build/win/dbghelp_xp/dbghelp.dll',
+        ],
+      },
+    }],
     ['OS=="win" and asan==1 and component=="shared_library"', {
       'variables': {
         'files': [
           '../third_party/llvm-build/Release+Asserts/lib/clang/3.7.0/lib/windows/clang_rt.asan_dynamic-i386.dll',
         ],
       },
     }],
     ['OS=="linux" and (asan==1 or lsan==1 or msan==1 or tsan==1)', {
       'variables': {
         'files': [
@@ skipping 50 matching lines @@
           '<(PRODUCT_DIR)/msvcr120.dll',
         ],
       },
     }],
     # Workaround for https://code.google.com/p/swarming/issues/detail?id=211
     ['asan==0 or lsan==0 or msan==0 or tsan==0', {
       'variables': {},
     }],
   ],
 }