[Cronet] Use developer_dir to find Xcode toolchain on official bots.

Bug: 774814
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I442f55b957017119b5241993ee0f90ae63a86557
Reviewed-on: https://chromium-review.googlesource.com/729126Reviewed-by: Andrei Kapishnikov <kapishnikov@chromium.org>
Commit-Queue: Misha Efimov <mef@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510231}

components/cronet/tools/hide_symbols.py

@@ -60,7 +60,7 @@ def main():
 
   if options.developer_dir:
     os.environ['DEVELOPER_DIR'] = options.developer_dir
-    developer_dir = options.developer_dir
+    developer_dir = options.developer_dir + '/Contents/Developer'
   else:
     developer_dir = subprocess.check_output(
         ['xcode-select', '--print-path']).strip()
@@ -68,6 +68,7 @@ def main():
   xctoolchain_libs = glob.glob(developer_dir
       + '/Toolchains/XcodeDefault.xctoolchain/usr/lib'
       + '/clang/*/lib/darwin/*.ios.a')
+  print "Adding xctoolchain_libs: ", xctoolchain_libs
 
   # ld -r concatenates multiple .o files and .a files into a single .o file,
   # while "hiding" symbols not marked as visible.