Add .gitignore files in build/ and third_party/

third_party/.gitignore

+# This file is needed for projects that has this directory as a separate Git
+# mirror in DEPS. Without it, a lot is wiped and re-downloaded for each sync.
+/__START__
+/accessibility-developer-tools/
+/accessibility_test_framework/lib/*.jar
+/adobe/flash/binaries
+/adobe/flash/symbols
+/amd/
+/android_protobuf/src
+/android_support_test_runner/lib/*.aar
+/android_support_test_runner/lib/*.jar
+/android_tools/
+/android_tools_internal/
+/android_webview_glue/src
+/angle
+/angle_dx11
+/apache-portable-runtime/src
+/apache_velocity/lib/*.jar
+/apache-win32/bin/*.exe
+/apache-win32/bin/*.dll
+/apache-win32/bin/iconv/*.so
+/apache-win32/modules/*.so
+/apache-win32/modules/*.dll
+/asan
+/bidichecker
+/bison
+/boringssl/src
+/bouncycastle/lib/*.jar
+/byte_buddy/lib/*.jar
+/cacheinvalidation/cacheinvalidation_unittests_run.xml
+/cardboard-java/src
+/catapult
+/ced/src
+/chromeos_login_manager
+/chromeos_text_input
+/chromite
+/cld_2/src
+/cld_3/src
+/colorama/src
+/cros
+/cros_system_api
+/custom_tabs_client/src
+/cygwin
+/deqp/src
+/directxsdk
+/dom_distiller_js/dist
+/drmemory/drmemory-windows-sfx.exe
+/drmemory/unpacked
+/elfutils/src
+/errorprone/lib
+/espresso/lib/*.jar
+/eyesfree/src
+/ffmpeg
+/findbugs
+/flac
+/flatbuffers/src
+/fontconfig/src
+/freetype-android/src
+/freetype2/src
+/gestures/gestures
+/gles2_conform
+/glslang/src
+/glslang-angle/src
+/gnu_binutils/
+/google_appengine_cloudstorage
+/google_toolbox_for_mac/src
+/googlemac
+/gvr-android-sdk/common_library.aar
+/gvr-android-sdk/libgvr_shim_static_arm.a
+/gvr-android-sdk/libgvr_shim_static_arm64.a
+/gvr-android-sdk/src
+/gperf
+/guava/lib/*.jar
+/hamcrest/lib/*.jar
+/hunspell_dictionaries
+/icu
+/icu4j/lib/*.jar
+/intellij/lib/*.jar
+/inspector_protocol
+/javax_inject/lib/*.jar
+/jsoncpp/source
+/jsr-305/src
+/junit/src
+/khronos_glcts
+/leakcanary/src
+/leveldatabase/src
+/leveldb
+/libc++-static/libc++.a
+/libaddressinput/src
+/libdrm/src
+/libevdev/src
+/libexif/sources
+/libFuzzer/src
+/libjingle/source
+/libjpeg_turbo
+/liblouis/src
+/libphonenumber/dist
+/libsrtp
+/libupnp
+/libvpx/source/libvpx
+/libwebm/source
+/libyuv
+/lighttpd
+/llvm
+/llvm-allocated-type
+/llvm-bootstrap
+/llvm-build
+/lss
+/mesa/src
+/mingw-w64
+/minigbm/src
+/mkl
+/mocha
+/mockito/src
+/nacl_sdk_binaries/
+/netty-tcnative/src
+/netty4/src
+/node/linux
+/node/mac
+/node/node_modules
+/node/*.tar.gz
+/node/win
+/nss
+/objenesis/lib/*.jar
+/omaha/src/omaha
+/openmax_dl/
+/openh264/src
+/ow2_asm/lib/*.jar
+/pdfsqueeze
+/pdfium
+/pefile
+/perl
+/ppapi
+/psyco_win32
+/pthreads-win32
+/py_trace_event/src
+/pyelftools
+/pyftpdlib/src
+/pylib
+/pymox/src
+/python_24
+/python_26
+/pywebsocket/src
+/pywebsocket/src
+/re2/src
+/requests/src
+/retrolambda/*.jar
+/robolectric/lib/*.jar
+/robolectric/robolectric
+/scan-build/src
+/scons-2.0.1
+/sfntly/src
+/shaderc/src
+/skia
+/smhasher/src
+/snappy/src
+/spirv-headers/src
+/SPIRV-Tools/src
+/spirv-tools-angle/src
+/sqlite4java/lib/**/*.dll
+/sqlite4java/lib/**/*.jar
+/sqlite4java/lib/**/*.jnilib
+/sqlite4java/lib/**/*.so
+/swiftshader/
+/syzygy
+/syzygy/binaries
+/tsan/
+/ub-uiautomator/lib
+/usb_ids
+/usrsctp/usrsctplib
+/v8-i18n
+/valgrind
+/vulkan-validation-layers/src
+/visualmetrics
+/wayland/src
+/wayland-protocols/src
+/wds/src
+/webdriver/pylib
+/webdriver/python/selenium
+/webgl
+/webgl/src
+/webpagereplay/
+/webrtc
+/widevine/cdm/chromeos
+/widevine/cdm/linux
+/widevine/cdm/mac
+/widevine/cdm/win
+/widevine/scripts
+/widevine/test/license_server
+/win_toolchain/.timestamps
+/win_toolchain/files
+/wix
+/xdg-utils
+/xulrunner-sdk
+/yasm/binaries
+/yasm/generate_files.xml
+/yasm/source/patched-yasm
+/yasm/yasm.xml
+