Change protoc build rule to not use cygwin bash.

build/protoc.gypi

 # Copyright (c) 2011 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.
 
-# This file is meant to be included into an target to provide a rule
+# This file is meant to be included into a target to provide a rule
 # to invoke protoc in a consistent manner.
 #
 # To use this, create a gyp target with the following form:
 # {
 #   'target_name': 'my_proto_lib',
 #   'type': 'static_library',
 #   'sources': [
 #     'foo.proto',
 #     'bar.proto',
 #   ],
@@ skipping 35 matching lines @@
       'inputs': [
         '<(protoc)',
       ],
       'outputs': [
         '<(py_dir)/<(RULE_INPUT_ROOT)_pb2.py',
         '<(cc_dir)/<(RULE_INPUT_ROOT).pb.cc',
         '<(cc_dir)/<(RULE_INPUT_ROOT).pb.h',
       ],
       'action': [
         '<(protoc)',
-        '--proto_path=<(proto_in_dir)',
+        # Using the --arg val form (instead of --arg=val) allows gyp's msvs rule
+        # generation to correct 'val' which is a path.
+        '--proto_path','<(proto_in_dir)',
         # Naively you'd use <(RULE_INPUT_PATH) here, but protoc requires
         # --proto_path is a strict prefix of the path given as an argument.
         '<(proto_in_dir)/<(RULE_INPUT_ROOT)<(RULE_INPUT_EXT)',
-        '--cpp_out=<(cc_dir)',
-        '--python_out=<(py_dir)',
+        '--cpp_out','<(cc_dir)',
+        '--python_out','<(py_dir)',
         ],
+      'msvs_cygwin_shell': 0,
       'message': 'Generating C++ and Python code from <(RULE_INPUT_PATH)',
       'process_outputs_as_sources': 1,
     },
   ],
   'dependencies': [
     '<(DEPTH)/third_party/protobuf/protobuf.gyp:protoc#host',
     '<(DEPTH)/third_party/protobuf/protobuf.gyp:protobuf_lite',
   ],
   'include_dirs': [
     '<(SHARED_INTERMEDIATE_DIR)/protoc_out',
   ],
   'direct_dependent_settings': {
     'include_dirs': [
       '<(SHARED_INTERMEDIATE_DIR)/protoc_out',
     ]
   },
   'export_dependent_settings': [
     # The generated headers reference headers within protobuf_lite,
     # so dependencies must be able to find those headers too.
     '<(DEPTH)/third_party/protobuf/protobuf.gyp:protobuf_lite',
   ],
   # This target exports a hard dependency because it generates header
   # files.
   'hard_dependency': 1,
 }