Adding option for Proguard jar to be switched.

build/config/android/rules.gni

Index: build/config/android/rules.gni
diff --git a/build/config/android/rules.gni b/build/config/android/rules.gni
index 6bc82e19f2c8a7a73f3bc69319cf5fd255099409..826d3f029a9a7e0c86bd5ca68044507408058c35 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -1278,9 +1278,11 @@ template("android_java_prebuilt") {
 #   requires_sdk_api_level_23: If defined and true, the apk is intended for
 #     installation only on Android M or later. In these releases the system
 #     linker does relocation unpacking, so we can enable it unconditionally.
-#   secondary_native_libs: the path of native libraries for secondary app abi.
+#   secondary_native_libs: The path of native libraries for secondary app abi.
 #   run_findbugs_override: Forces run_findbugs on or off. If undefined, the
 #     default will use the build arg run_findbugs.
+#   proguard_jar_path: The path to proguard.jar you wish to use. If undefined,
+#     the proguard used will be the checked in one in //third_party/proguard.
 #
 # Example
 #   android_apk("foo_apk") {
@@ -1437,7 +1439,7 @@ template("android_apk") {
   _proguard_enabled =
       defined(invoker.proguard_enabled) && invoker.proguard_enabled
   if (_proguard_enabled) {
-    _proguard_jar_path = "$base_path.proguard.jar"
+    _proguard_output_jar_path = "$base_path.proguard.jar"
   }
 
   _emma_never_instrument = defined(invoker.testonly) && invoker.testonly
@@ -1472,7 +1474,7 @@ template("android_apk") {
 
     proguard_enabled = _proguard_enabled
     if (_proguard_enabled) {
-      proguard_info = "$_proguard_jar_path.info"
+      proguard_info = "$_proguard_output_jar_path.info"
     }
 
     native_libs = _native_libs
@@ -1558,6 +1560,9 @@ template("android_apk") {
       if (enable_multidex) {
         defines += [ "ENABLE_MULTIDEX" ]
       }
+      if (is_java_debug) {
+        defines += [ "DEBUG" ]
+      }
     }
     _srcjar_deps += [ ":${_template_name}__build_config_java" ]
   }
@@ -1629,7 +1634,11 @@ template("android_apk") {
     }
     _proguard_target = "${_template_name}__proguard"
     proguard(_proguard_target) {
-      forward_variables_from(invoker, [ "alternative_android_sdk_jar" ])
+      forward_variables_from(invoker,
+                             [
+                               "alternative_android_sdk_jar",
+                               "proguard_jar_path",
+                             ])
       deps = [
         ":$build_config_target",
         ":$java_target",
@@ -1640,7 +1649,7 @@ template("android_apk") {
                  _jar_path,
                ] + _proguard_configs
 
-      output_jar_path = _proguard_jar_path
+      output_jar_path = _proguard_output_jar_path
       _rebased_proguard_configs = rebase_path(_proguard_configs, root_build_dir)
       args = [
         "--proguard-configs=$_rebased_proguard_configs",
@@ -1659,7 +1668,7 @@ template("android_apk") {
         args += [ "--tested-apk-info=@FileArg($_rebased_apk_under_test_build_config:deps_info:proguard_info)" ]
       }
     }
-    _dex_sources = [ _proguard_jar_path ]
+    _dex_sources = [ _proguard_output_jar_path ]
     _dex_deps = [ ":$_proguard_target" ]
   } else {
     if (enable_multidex) {