Copy libvpx from DEPS to src

WATCHLISTS

Index: WATCHLISTS
diff --git a/WATCHLISTS b/WATCHLISTS
index bea74b644d74f9ea1e7da96c1151b199fb27e6c2..37c6928f13b73964b24438cdee7d4d28583153a0 100644
--- a/WATCHLISTS
+++ b/WATCHLISTS
@@ -446,6 +446,9 @@
     'libwebp': {
       'filepath': 'third_party/libwebp'
     },
+    'libvpx': {
+      'filepath': 'third_party/libvpx'
+    },
     'linux_fonts': {
       'filepath': 'ui/gfx/font_render_params_.*|'\
                   'ui/gfx/platform_font_linux.*|'\
@@ -1021,6 +1024,8 @@
     'ipc': ['jam@chromium.org', 'darin-cc@chromium.org'],
     'libwebp': ['urvang@chromium.org', 'jzern@chromium.org',
                 'skal@google.com', 'vikasa@google.com'],
+    'libvpx': ['tomfinegan@chromium.org', 'jzern@chromium.org',
+               'fgalligan@chromium.org', 'johannkoenig@chromium.org'],
     'linux_fonts': ['derat+watch@chromium.org'],
     'linux_sandboxing': ['jln+watch@chromium.org'],
     'linux_seccomp_bpf': ['jln+watch@chromium.org'],