Make update_dart_sdk.sh prettier and more resilient

bin/cache/update_dart_sdk.sh

@@ -3,12 +3,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+set -e
+
 DART_SDK_PATH="$FLUTTER_ROOT/bin/cache/dart-sdk"
 DART_SDK_STAMP_PATH="$FLUTTER_ROOT/bin/cache/dart-sdk.stamp"
 DART_SDK_VERSION=`cat "$FLUTTER_ROOT/bin/cache/dart-sdk.version"`
 
 if [ ! -f "$DART_SDK_STAMP_PATH" ] || [ "$DART_SDK_VERSION" != `cat "$DART_SDK_STAMP_PATH"` ]; then
-  echo Downloading Dart SDK $DART_SDK_VERSION...
+  echo "Downloading Dart SDK $DART_SDK_VERSION..."
 
   case "$(uname -s)" in
     Darwin)
@@ -25,12 +27,12 @@ if [ ! -f "$DART_SDK_STAMP_PATH" ] || [ "$DART_SDK_VERSION" != `cat "$DART_SDK_S
 
   DART_SDK_URL="http://gsdview.appspot.com/dart-archive/channels/stable/raw/$DART_SDK_VERSION/sdk/$DART_ZIP_NAME"
 
-  rm -rf "$DART_SDK_PATH"
-  mkdir -p "$DART_SDK_PATH"
+  rm -rf -- "$DART_SDK_PATH"
+  mkdir -p -- "$DART_SDK_PATH"
   DART_SDK_ZIP="$FLUTTER_ROOT/bin/cache/dart-sdk.zip"
 
-  curl -C - --location -o "$DART_SDK_ZIP" "$DART_SDK_URL"
+  curl --progress-bar -continue-at=- --location --output "$DART_SDK_ZIP" "$DART_SDK_URL"
   unzip -o -q "$DART_SDK_ZIP" -d "$FLUTTER_ROOT/bin/cache"
-  rm "$DART_SDK_ZIP"
-  echo $DART_SDK_VERSION > "$DART_SDK_STAMP_PATH"
+  rm -f -- "$DART_SDK_ZIP"
+  echo "$DART_SDK_VERSION" > "$DART_SDK_STAMP_PATH"
 fi