Skip toolchain downloads for a few android tools

platform_tools/android/bin/android_setup.sh

 #!/bin/bash
 ###############################################################################
 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 ###############################################################################
 #
 # android_setup.sh: Sets environment variables used by other Android scripts.
 
@@ skipping 144 matching lines @@
       DEFINES="${DEFINES} skia_arch_type=${ANDROID_ARCH-arm}"
       # If ANDROID_IGNORE_UNKNOWN_DEVICE is set, extra gyp defines can be
       # added via ANDROID_GYP_DEFINES
       DEFINES="${DEFINES} ${ANDROID_GYP_DEFINES}"
       ;;
   esac
 
   verbose "The build is targeting the device: $TARGET_DEVICE"
   exportVar DEVICE_ID $TARGET_DEVICE
 
-  # setup the appropriate cross compiling toolchains
-  source $SCRIPT_DIR/utils/setup_toolchain.sh
+  if [ -z "$SKIP_TOOLCHAIN_SETUP" ]; then
+    # setup the appropriate cross compiling toolchains
+    source $SCRIPT_DIR/utils/setup_toolchain.sh
+  fi
 
   DEFINES="${DEFINES} android_toolchain=${TOOLCHAIN_TYPE}"
   DEFINES="${DEFINES} android_buildtype=${BUILDTYPE}"
   exportVar GYP_DEFINES "$DEFINES $GYP_DEFINES"
 
   SKIA_SRC_DIR=$(cd "${SCRIPT_DIR}/../../.."; pwd)
   DEFAULT_SKIA_OUT="${SKIA_SRC_DIR}/out/config/android-${TARGET_DEVICE}"
   exportVar SKIA_OUT "${SKIA_OUT:-${DEFAULT_SKIA_OUT}}"
 }
 
@@ skipping 88 matching lines @@
       $ADB $DEVICE_SERIAL shell mkdir -p "$(dirname "$ANDROID_DST")"
       $ADB $DEVICE_SERIAL push $HOST_SRC $ANDROID_DST
     fi
   fi
 
   # turn error checking back on
   set -e
 }
 
 setup_device "${DEVICE_ID}"