Use proguard.cfg in cronet sample apk.

components/cronet.gypi

Index: components/cronet.gypi
diff --git a/components/cronet.gypi b/components/cronet.gypi
index a68819dbe0cd9a739f31d24dd1dea95a0d1749aa..f9ef3dc76466810de8e60f441c58c6c07cf0d451 100644
--- a/components/cronet.gypi
+++ b/components/cronet.gypi
@@ -331,12 +331,19 @@
           'type': 'none',
           'dependencies': [
             'cronet',
+            'cronet_stub',
           ],
           'variables': {
             'apk_name': 'CronetSample',
             'java_in_dir': 'cronet/android/sample',
             'resource_dir': 'cronet/android/sample/res',
             'native_lib_target': 'libcronet',
+            'proguard_enabled': 'true',
+            'proguard_flags_paths': [
+              'cronet/android/proguard.cfg',
+              # Proguard config for instrumentation test apk.
+              'cronet/android/sample/javatests/proguard.cfg',
+            ],
           },
           'includes': [ '../build/java_apk.gypi' ],
         },
@@ -357,7 +364,9 @@
           'target_name': 'cronet_sample_test_apk',
           'type': 'none',
           'dependencies': [
+            'cronet',
             'cronet_sample_apk_java',
+            'cronet_stub',
             '../base/base.gyp:base_java',
             '../base/base.gyp:base_javatests',
             '../base/base.gyp:base_java_test_support',
@@ -368,6 +377,7 @@
           'variables': {
             'apk_name': 'CronetSampleTest',
             'java_in_dir': 'cronet/android/sample/javatests',
+            'proguard_enabled': 'true',
             'resource_dir': 'cronet/android/sample/res',
             'is_test_apk': 1,
           },