Add rtc_use_memcheck flag, update MB and GN to handle it, and add gni files listing the runtime deps

tools/valgrind-webrtc/valgrind-webrtc.gni

Index: tools/valgrind-webrtc/valgrind-webrtc.gni
diff --git a/tools/valgrind-webrtc/valgrind-webrtc.gni b/tools/valgrind-webrtc/valgrind-webrtc.gni
new file mode 100644
index 0000000000000000000000000000000000000000..1a5b8dea373d43ad89128a94fb77c9ccee8b5685
--- /dev/null
+++ b/tools/valgrind-webrtc/valgrind-webrtc.gni
@@ -0,0 +1,32 @@
+# Copyright (c) 2016 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.
+
+# TODO(ehmaldonado): Replace by the new paths once the upstream changes land.
+# See https://codereview.chromium.org/2526883002/ for valgrind-binaries.gni and
+# https://codereview.chromium.org/2517953007/ for python-google.gni and
+# valgrind.gni
+import("python-google.gni")
+import("valgrind-binaries.gni")
+import("valgrind.gni")
+
+valgrind_webrtc_dependencies = [
+  "../../tools/valgrind-webrtc/gtest_exclude/modules_tests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/modules_unittests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/peerconnection_unittests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/rtc_media_unittests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/rtc_media_unittests.gtest-memcheck_mac.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/rtc_pc_unittests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/rtc_unittests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/video_engine_tests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/gtest_exclude/webrtc_nonparallel_tests.gtest-memcheck.txt",
+  "../../tools/valgrind-webrtc/memcheck/suppressions.txt",
+  "../../tools/valgrind-webrtc/memcheck/suppressions_mac.txt",
+  "../../tools/valgrind-webrtc/memcheck/suppressions_win32.txt",
+  "../../tools/valgrind-webrtc/webrtc_tests.py",
+  "../../tools/valgrind-webrtc/webrtc_tests.sh",
+] + valgrind_dependencies + valgrind_binaries + python_google