win: Add and use a custom CaptureContext() implementation

util/util.gyp

Index: util/util.gyp
diff --git a/util/util.gyp b/util/util.gyp
index 099c3103d272d26685edff857348085b2dcad614..dab345ac27ac8206e70211aff8894a57c753da7e 100644
--- a/util/util.gyp
+++ b/util/util.gyp
@@ -149,6 +149,8 @@
         'thread/thread_posix.cc',
         'thread/thread_win.cc',
         'win/address_types.h',
+        'win/capture_context.asm',
+        'win/capture_context.h',
         'win/checked_win_address_range.h',
         'win/exception_handler_server.cc',
         'win/exception_handler_server.h',
@@ -240,6 +242,41 @@
               '-lwinhttp.lib',
             ],
           },
+          'conditions': [
+            ['target_arch=="ia32"', {
+              'msvs_settings': {
+                'MASM': {
+                  'UseSafeExceptionHandlers': 'true',
+                },
+              },
+            }],
+            ['target_arch=="x64"', {
+              'rules': [
+                {
+                  # .asm files aren’t assembled by the Windows toolchain by
+                  # default on x86_64.
+                  'rule_name': 'Assemble',
+                  'msvs_cygwin_shell': 0,
+                  'msvs_quote_cmd': 0,
+                  'extension': 'asm',
+                  'inputs': [],
+                  'outputs': [
+                    '<(INTERMEDIATE_DIR)/<(RULE_INPUT_ROOT).obj',
+                  ],
+                  'action': [
+                    'ml64',
+                    '/nologo',
+                    '/Fo',
+                    '<(INTERMEDIATE_DIR)\\<(RULE_INPUT_ROOT).obj',
+                    '/c',
+                    '<(RULE_INPUT_PATH)',
+                  ],
+                  'process_outputs_as_sources': 1,
+                  'message': 'Assembling <(RULE_INPUT_PATH)',
+                },
+              ],
+            }],
+          ],
         }],
       ],
     },