Fix gradle initial dependency fetch on windows

R=jmhenaff@google.com, sgjesse@google.com

Bug:
Change-Id: I19ed128b61b1506279742b961fbce05cc57abcfb
diff --git a/tools/gradle.py b/tools/gradle.py
index 64e6d51..f30b3f4 100755
--- a/tools/gradle.py
+++ b/tools/gradle.py
@@ -14,7 +14,7 @@
 
 GRADLE_DIR = os.path.join(utils.REPO_ROOT, 'third_party', 'gradle')
 GRADLE_SHA1 = os.path.join(GRADLE_DIR, 'gradle.tar.gz.sha1')
-if os.name == 'nt':
+if utils.IsWindows():
   GRADLE = os.path.join(GRADLE_DIR, 'gradle', 'bin', 'gradle.bat')
 else:
   GRADLE = os.path.join(GRADLE_DIR, 'gradle', 'bin', 'gradle')