Reland "Android: Allow proguard to strip unused native methods."

Reland of dc8f3c0a.

chrome_public_test_apk is now merged with chrome_public_apk_for_test
which should fix the proguard issue.

TBR: agrieve@chromium.org
Bug: 688465
Change-Id: Ie43eae7f945e5ae444f1cb0adc0703b334402f3c
Reviewed-on: https://chromium-review.googlesource.com/c/1333988Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608038}

base/android/proguard/chromium_code.flags

@@ -38,9 +38,6 @@
 -keepclasseswithmembers class * {
   @org.chromium.base.annotations.UsedByReflection <fields>;
 }
--keepclasseswithmembers,includedescriptorclasses class * {
-  native <methods>;
-}
 
 # Remove methods annotated with this if their return value is unused.
 -assumenosideeffects class ** {

base/android/proguard/explicit_jni_registration.flags

+# Copyright 2018 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# -keepclasseswithmembers rather than -keepclasseswithmembernames to avoid
+# shrinking of unused native methods. Explicit JNI registration requires even
+# unused classes to be present during RegisterNatives().
+-keepclasseswithmembers,includedescriptorclasses class * {
+  native <methods>;
+}

base/android/proguard/implicit_jni_registration.flags

+# Copyright 2018 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# -keepclasseswithmembernames rather than -keepclasseswithmembers to allow
+# shrinking of unused native methods.
+-keepclasseswithmembernames,includedescriptorclasses class * {
+  native <methods>;
+}

build/config/android/rules.gni

@@ -2433,6 +2433,13 @@ if (enable_java_templates) {
           proguard_configs += [ "//build/android/multidex.flags" ]
         }
         proguard_mapping_path = _proguard_mapping_path
+        if (_use_chromium_linker) {
+          proguard_configs +=
+              [ "//base/android/proguard/explicit_jni_registration.flags" ]
+        } else {
+          proguard_configs +=
+              [ "//base/android/proguard/implicit_jni_registration.flags" ]
+        }
       }
 
       # Don't depend on the runtime_deps target in order to avoid having to

components/cronet/android/BUILD.gn

@@ -470,6 +470,7 @@ action("cronet_combine_proguard_flags") {
   script = "//components/cronet/tools/generate_proguard_file.py"
   sources = [
     "//base/android/proguard/chromium_code.flags",
+    "//base/android/proguard/explicit_jni_registration.flags",
     "//components/cronet/android/cronet_impl_native_proguard.cfg",
   ]
   outputs = [