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

This reverts commit dc8f3c0a.

Reason for revert: Casing failures
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/android-rel/2442

Original change's description:
> Android: Allow proguard to strip unused native methods.
> 
> This CL changes Monochrome APKs to allow proguard to strip out Java
> native methods that aren't used.
> 
> For APKs that use explicit JNI registration, this isn't possible since
> RegisterNatives ends up trying to load classes that are unused and
> removed by proguard.
> 
> Bug: 688465
> Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;master.tryserver.chromium.android:android_cronet_tester
> Change-Id: I6816bd68ce47e59bfc9f75dace1b34ab3c200222
> Reviewed-on: https://chromium-review.googlesource.com/1244605
> Reviewed-by: Paul Jensen <pauljensen@chromium.org>
> Reviewed-by: agrieve <agrieve@chromium.org>
> Commit-Queue: Eric Stevenson <estevenson@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#594743}

TBR=pauljensen@chromium.org,agrieve@chromium.org,estevenson@chromium.org

Change-Id: Ic8e1f808a63c9c0fd119ee36efa1cc2b1e9a0616
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 688465
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;master.tryserver.chromium.android:android_cronet_tester
Reviewed-on: https://chromium-review.googlesource.com/1249825Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594774}

base/android/proguard/chromium_code.flags

@@ -38,6 +38,9 @@
 -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

@@ -2400,13 +2400,6 @@ if (enable_java_templates) {
         if (_enable_multidex) {
           proguard_configs += [ "//build/android/multidex.flags" ]
         }
-        if (_use_chromium_linker) {
-          proguard_configs +=
-              [ "//base/android/proguard/explicit_jni_registration.flags" ]
-        } else {
-          proguard_configs +=
-              [ "//base/android/proguard/implicit_jni_registration.flags" ]
-        }
         proguard_output_jar_path = _proguard_output_jar_path
       }
 

components/cronet/android/BUILD.gn

@@ -471,7 +471,6 @@ 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 = [