Make blink_trybot recipe work on windows

scripts/slave/recipes/android_webview_aosp.expected/does_delete_stale_chromium.json

 [
   {
-   "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "config", "--spec", "deps_os = {}\nhooks = []\nsolutions = [{'custom_deps': {}, 'custom_vars': {}, 'deps_file': '', 'managed': True, 'name': 'src', 'safesync_url': None, 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]\ntarget_os = []\ntarget_os_only = False"],
+   "cmd": ["python", "-u", "[DEPOT_TOOLS_ROOT]/gclient.py", "config", "--spec", "deps_os = {}\nhooks = []\nsolutions = [{'custom_deps': {}, 'custom_vars': {}, 'deps_file': '', 'managed': True, 'name': 'src', 'safesync_url': None, 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]\ntarget_os = []\ntarget_os_only = False"],
    "name": "[spec: empty_deps] gclient setup",
    "seed_steps": ["[spec: empty_deps] gclient setup", "[spec: empty_deps] gclient revert", "[spec: empty_deps] gclient sync"]
   },
   {
-   "cmd": ["python", "[BUILD_ROOT]/scripts/slave/gclient_safe_revert.py", ".", "[DEPOT_TOOLS_ROOT]/gclient"],
+   "cmd": ["python", "-u", "[BUILD_ROOT]/scripts/slave/gclient_safe_revert.py", ".", "[DEPOT_TOOLS_ROOT]/gclient"],
    "name": "[spec: empty_deps] gclient revert"
   },
   {
-   "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "sync", "--nohooks", "--revision", "src@204787"],
+   "cmd": ["python", "-u", "[DEPOT_TOOLS_ROOT]/gclient.py", "sync", "--nohooks", "--revision", "src@204787"],
    "name": "[spec: empty_deps] gclient sync"
   },
   {
    "cmd": ["[SLAVE_BUILD_ROOT]/src/android_webview/buildbot/deps_whitelist.py", "--method", "android_build", "--path-to-deps", "[SLAVE_BUILD_ROOT]/src/DEPS", "--output-json", "/path/to/tmp/json"],
    "name": "calculate trimmed deps"
   },
   {
-   "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "config", "--spec", "deps_os = {}\nhooks = []\nsolutions = [{'custom_deps': {'src/blacklist/project/1': None, 'src/blacklist/project/2': None}, 'custom_vars': {}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'safesync_url': None, 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]\ntarget_os = ['android']\ntarget_os_only = False"],
+   "cmd": ["python", "-u", "[DEPOT_TOOLS_ROOT]/gclient.py", "config", "--spec", "deps_os = {}\nhooks = []\nsolutions = [{'custom_deps': {'src/blacklist/project/1': None, 'src/blacklist/project/2': None}, 'custom_vars': {}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'safesync_url': None, 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]\ntarget_os = ['android']\ntarget_os_only = False"],
    "name": "[spec: trimmed] gclient setup",
    "seed_steps": ["[spec: trimmed] gclient setup", "[spec: trimmed] gclient revert", "[spec: trimmed] gclient sync"]
   },
   {
-   "cmd": ["python", "[BUILD_ROOT]/scripts/slave/gclient_safe_revert.py", ".", "[DEPOT_TOOLS_ROOT]/gclient"],
+   "cmd": ["python", "-u", "[BUILD_ROOT]/scripts/slave/gclient_safe_revert.py", ".", "[DEPOT_TOOLS_ROOT]/gclient"],
    "name": "[spec: trimmed] gclient revert"
   },
   {
-   "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "sync", "--nohooks", "--revision", "src@204787"],
+   "cmd": ["python", "-u", "[DEPOT_TOOLS_ROOT]/gclient.py", "sync", "--nohooks", "--revision", "src@204787"],
    "name": "[spec: trimmed] gclient sync"
   },
   {
    "cmd": ["[SLAVE_BUILD_ROOT]/src/build/util/lastchange.py", "-o", "[SLAVE_BUILD_ROOT]/src/build/util/LASTCHANGE", "-s", "[SLAVE_BUILD_ROOT]/src"],
    "name": "Chromium LASTCHANGE",
    "seed_steps": ["Chromium LASTCHANGE", "Blink LASTCHANGE"]
   },
   {
    "cmd": ["[SLAVE_BUILD_ROOT]/src/build/util/lastchange.py", "-o", "[SLAVE_BUILD_ROOT]/src/build/util/LASTCHANGE.blink", "-s", "[SLAVE_BUILD_ROOT]/src/third_party/WebKit"],
    "name": "Blink LASTCHANGE"
@@ skipping 29 matching lines @@
    "cmd": ["[BUILD_ROOT]/scripts/slave/android/with_lunch", "[SLAVE_BUILD_ROOT]/android-src", "full-eng", "[SLAVE_BUILD_ROOT]/android-src/external/chromium_org/android_webview/tools/gyp_webview"],
    "cwd": "[SLAVE_BUILD_ROOT]/android-src/external/chromium_org",
    "name": "gyp_webview"
   },
   {
    "cmd": ["[BUILD_ROOT]/scripts/slave/android/with_lunch", "[SLAVE_BUILD_ROOT]/android-src", "full-eng", "[BUILD_ROOT]/scripts/slave/compile.py", "libwebviewchromium", "android_webview_java", "--build-dir", "[SLAVE_BUILD_ROOT]", "--src-dir", "[SLAVE_BUILD_ROOT]/android-src", "--build-tool", "make-android", "--verbose"],
    "cwd": "[SLAVE_BUILD_ROOT]",
    "name": "compile"
   }
 ]