Introduce WPTServe for running W3C Blink Layout tests

Tools/Scripts/webkitpy/layout_tests/servers/wpt_support/checkout.sh

+#!/bin/bash
+#
+# Removes ./wpt/ directory containing the reduced web-platform-tests tree and
+# starts a new checkout. Only files in WPTWhiteList are retained. The revisions
+# getting checked out are defined in WPTHeads.
+
+DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+cd $DIR
+TARGET_DIR=$DIR/wpt
+REMOTE_REPO="https://chromium.googlesource.com/external/w3c/web-platform-tests.git"
+
+# First line is the main repo HEAD.
+WPT_HEAD=$(head -n 1 $DIR/WPTHeads)
+
+# Remove if already exists.
+[ -d "$TARGET_DIR" ] && rm -rf $TARGET_DIR
+
+# Clone the entire thingy.
+git clone $REMOTE_REPO $TARGET_DIR
+cd $TARGET_DIR && git checkout $WPT_HEAD
+
+# Grab all submodules.
+
+# First line is the main repo HEAD, so skip it to get the submodules only.
+tail -n+2 $DIR/WPTHeads | while read dir submodule commit; do
+  echo
+  echo "Working in $dir on submodule $submodule. Setting head to: $commit"
+  cd $TARGET_DIR/$dir && \
+    git submodule update --init $submodule && \
+    cd $TARGET_DIR/$dir/$submodule && \
+    git checkout $commit
+done
+
+# Remove all except white-listed.
+cd $TARGET_DIR
+find . -type f | grep -Fxvf ../WPTWhiteList | xargs -n 1 rm
+find . -empty -type d -delete
+
+# Fix up mod_pywebsocket dependency.
+match_line="from mod_pywebsocket import standalone as pywebsocket"
+prepend_line="sys.path.insert(0, os.path.abspath(os.path.join('..', '..', '..', '..', '..', 'webkitpy', 'thirdparty')))"
+sed  -i "/$match_line/i $prepend_line" $TARGET_DIR/tools/serve/serve.py
+
+# Remove the .git dirs.
+rm -rf $TARGET_DIR/.git \
+       $TARGET_DIR/tools/.git \
+       $TARGET_DIR/tools/wptserve/.git \
+       $TARGET_DIR/tools/pywebsocket/.git \
+
+# TODO(burnik): Handle the SSL certs.