veryron_rilato-chrome-pfq has been failing for missing <X11/keysymdef.h> since 5/1/2016.

https://chromegw.corp.google.com/i/chromeos/builders/veyron_rialto-chrome-pfq/builds/53

The error is seen in the log:
https://chromegw.corp.google.com/i/chromeos/builders/veyron_rialto-chrome-pfq/builds/53/steps/SimpleChromeWorkflow/logs/stdio

FAILED: obj/remoting/host/linux/remoting_host.unicode_to_keysym.o 
armv7a-cros-linux-gnueabi-g++ -B/tmp/cbuildbot-tmpIKMqYc/chrome-sdk-cacheDKi3Ud/cache/chrome-sdk/tarballs/veyron_rialto+__b__cbuild__internal_master__buildbot_archive__veyron_rialto-chrome-pfq__R52-8269.0.0-rc1+target_toolchain/usr/x86_64-pc-linux-gnu/armv7a-cros-linux-gnueabi/binutils-bin/2.25.51-gold -MMD -MF obj/remoting/host/linux/remoting_host.unicode_to_keysym.o.d -DBINARY_CORE=1 -DBINARY_DESKTOP=2 -DBINARY_HOST_ME2ME=3 -DBINARY_NATIVE_MESSAGING_HOST=4 -DBINARY_REMOTE_ASSISTANCE_HOST=5 -DV8_DEPRECATION_WARNINGS -D_FILE_OFFSET_BITS=64 -DCHROMIUM_BUILD -DCR_CLANG_REVISION=267383-1 -DCOMPONENT_BUILD -DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1 -DUSE_ASH=1 -DUSE_PANGO=1 -DUSE_CAIRO=1 -DUSE_CRAS=1 -DUSE_OZONE=1 -DUSE_DEFAULT_RENDER_THEME=1 -DUSE_LIBJPEG_TURBO=1 -DIMAGE_LOADER_EXTENSION=1 -DENABLE_WEBRTC=1 -DENABLE_MEDIA_ROUTER=1 -DENABLE_PEPPER_CDMS -DENABLE_NOTIFICATIONS -DENABLE_TOPCHROME_MD=1 -DENABLE_WAYLAND_SERVER=1 -DUSE_UDEV -DFIELDTRIAL_TESTING_ENABLED -DENABLE_TASK_MANAGER=1 -DENABLE_EXTENSIONS=1 -DENABLE_PDF=1 -DENABLE_PLUGINS=1 -DENABLE_SESSION_SERVICE=1 -DENABLE_THEMES=1 -DENABLE_AUTOFILL_DIALOG=1 -DENABLE_PRINTING=1 -DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1 -DENABLE_CAPTIVE_PORTAL_DETECTION=1 -DENABLE_APP_LIST=1 -DENABLE_SUPERVISED_USERS=1 -DENABLE_MDNS=1 -DENABLE_SERVICE_DISCOVERY=1 -DV8_USE_EXTERNAL_STARTUP_DATA -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -D__ARMEL__ -D__arm__ -DNVALGRIND '-DHOST_BUNDLE_NAME="ChromotingHost.bundle"' '-DPREFPANE_BUNDLE_NAME="Chromoting.prefPane"' -DVERSION=52.0.2722.0 -DTOOLKIT_VIEWS=1 -DMOJO_USE_SYSTEM_IMPL -DPROTOBUF_USE_DLLS -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DFEATURE_ENABLE_SSL -DFEATURE_ENABLE_VOICEMAIL -DEXPAT_RELATIVE_PATH -DGTEST_RELATIVE_PATH -DNO_MAIN_THREAD_WRAPPING -DNO_SOUND_SYSTEM -DLINUX -DWEBRTC_LINUX -DWEBRTC_POSIX -DCHROMEOS -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_NOEXCEPT= -DSKIA_DLL -DGR_GL_IGNORE_ES3_MSAA=0 -DSK_SUPPORT_GPU=1 -DSK_IGNORE_LINEONLY_AA_CONVEX_PATH_OPTS -DWEBRTC_CHROMIUM_BUILD -DUSE_LIBPCI=1 -DUSE_NSS_CERTS=1 -DOS_CHROMEOS=1 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DNDEBUG -DDYNAMIC_ANNOTATIONS_ENABLED=0 -I../.. -Igen -I../../third_party/skia/include/utils -I../../third_party/khronos -I../../gpu -I../../skia/config -Igen/angle -I../../third_party/WebKit/Source -I../../third_party/protobuf/src -Igen/protoc_out -I../../third_party/webrtc_overrides -I../../third_party/libjingle/overrides -I../../third_party/libjingle/source -I../../testing/gtest/include -I../../third_party -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -Igen/policy -I../../skia/ext -I../../third_party/skia/include/core -I../../third_party/skia/include/effects -I../../third_party/skia/include/pdf -I../../third_party/skia/include/gpu -I../../third_party/skia/include/lazy -I../../third_party/skia/include/pathops -I../../third_party/skia/include/pipe -I../../third_party/skia/include/ports -Igen/ui/views/resources -Werror -pthread -fno-strict-aliasing -Wall -Wno-extra -Wno-unused-parameter -Wno-missing-field-initializers -fvisibility=hidden -pipe -fPIC -Wno-unused-local-typedefs -I/tmp/cbuildbot-tmpIKMqYc/chrome-sdk-cacheDKi3Ud/cache/chrome-sdk/tarballs/veyron_rialto+__b__cbuild__internal_master__buildbot_archive__veyron_rialto-chrome-pfq__R52-8269.0.0-rc1+sysroot_chromeos-base_chromeos-chrome.tar.xz/usr/include/nss -I/tmp/cbuildbot-tmpIKMqYc/chrome-sdk-cacheDKi3Ud/cache/chrome-sdk/tarballs/veyron_rialto+__b__cbuild__internal_master__buildbot_archive__veyron_rialto-chrome-pfq__R52-8269.0.0-rc1+sysroot_chromeos-base_chromeos-chrome.tar.xz/usr/include/nspr -Wno-maybe-uninitialized -march=armv7-a -mtune=generic-armv7-a -mfpu=neon -mfloat-abi=hard -mthumb --sysroot=/tmp/cbuildbot-tmpIKMqYc/chrome-sdk-cacheDKi3Ud/cache/chrome-sdk/tarballs/veyron_rialto+__b__cbuild__internal_master__buildbot_archive__veyron_rialto-chrome-pfq__R52-8269.0.0-rc1+sysroot_chromeos-base_chromeos-chrome.tar.xz -O2 -fno-ident -fdata-sections -ffunction-sections -funwind-tables -g -pipe -march=armv7-a -mtune=cortex-a15 -mfpu=neon -mfloat-abi=hard -D__google_stl_debug_vector=1 -gsplit-dwarf -fno-exceptions -fno-rtti -fno-threadsafe-statics -fvisibility-inlines-hidden -Wno-abi -std=gnu++11 -Wno-narrowing -Wno-literal-suffix  -c ../../remoting/host/linux/unicode_to_keysym.cc -o obj/remoting/host/linux/remoting_host.unicode_to_keysym.o
../../remoting/host/linux/unicode_to_keysym.cc:27:27: fatal error: X11/keysymdef.h: No such file or directory
 #include <X11/keysymdef.h>
                           ^
compilation terminated.

I guess something might be changed in veyron-rialto ebuild overlay so that this is no longer included in the build package? Since veyron-rialto is a headless device, so maybe the X11 is removed from the ebuild?