[Cronet] Use xcode clang on iOS to reduce release binary size.

BUG=666502
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_cronet_tester

Review-Url: https://codereview.chromium.org/2614423002
Cr-Commit-Position: refs/heads/master@{#471077}

components/cronet/tools/cr_cronet.py

@@ -80,7 +80,8 @@ def main():
   if is_os:
     target_os = 'ios'
     test_target = 'cronet_test'
-    gn_args = 'is_cronet_build=true is_component_build=false '
+    gn_args = 'is_cronet_build=true is_component_build=false ' \
+        'use_xcode_clang=true '
     gn_extra = '--ide=xcode'
     if options.iphoneos:
       gn_args += ' target_cpu="arm64" '

components/cronet/tools/package_ios.py

@@ -90,8 +90,8 @@ def package_ios_framework_using_gn(out_dir='out/Framework', extra_options=''):
   # Package all builds in the output directory
   os.makedirs(out_dir)
   build_dir = ''
-  for (build_config, gn_extra_args) in [('Debug', 'is_debug=true'),
-        ('Release', 'is_debug=false enable_stripping=true')]:
+  for (build_config, gn_extra_args) in [('Debug', 'is_debug=true use_xcode_clang=true'),
+        ('Release', 'is_debug=false enable_stripping=true is_official_build=true')]:
     for (target_device, target_cpu, additional_cpu) in [('os', 'arm', 'arm64'),
         ('simulator', 'x86', 'x64')]:
       target_dir = '%s-iphone%s' % (build_config, target_device)