Add build_protobuf variable.

webrtc/build/protoc.gypi

 # Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # Copied from Chromium's src/build/protoc.gypi
 #
@@ skipping 91 matching lines @@
         '--use-system-protobuf=<(use_system_protobuf)',
         '--',
         '<(protoc)',
         '--cpp_out', '<(cc_generator_options)<(cc_dir)',
         '--python_out', '<(py_dir)',
       ],
       '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',
     '<(DEPTH)',
   ],
   'direct_dependent_settings': {
     'include_dirs': [
       '<(SHARED_INTERMEDIATE_DIR)/protoc_out',
       '<(DEPTH)',
     ]
   },
-  '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,
+  'conditions': [
+    ['build_protobuf==1', {
+      'dependencies': [
+        '<(DEPTH)/third_party/protobuf/protobuf.gyp:protoc#host',
+        '<(DEPTH)/third_party/protobuf/protobuf.gyp:protobuf_lite',
+      ],
+      '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',
+      ],
+    }],
+  ],
 }