[Cronet] add base proguard flags

components/cronet/android/BUILD.gn

Index: components/cronet/android/BUILD.gn
diff --git a/components/cronet/android/BUILD.gn b/components/cronet/android/BUILD.gn
index 99485b52af894a15928f64f36a3706c6e68f2de4..8e2b72fb3aec8ac0d4285324cca9ca5baf29b7d8 100644
--- a/components/cronet/android/BUILD.gn
+++ b/components/cronet/android/BUILD.gn
@@ -401,6 +401,7 @@ android_apk("cronet_sample_apk") {
     proguard_configs = [
       "proguard.cfg",
       "sample/javatests/proguard.cfg",
+      "//base/android/base_proguard_config.flags",
     ]
   }
 }
@@ -716,6 +717,7 @@ android_apk("cronet_perf_test_apk") {
   proguard_configs = [
     "proguard.cfg",
     "test/javaperftests/proguard.cfg",
+    "//base/android/base_proguard_config.flags",
   ]
 }
 
@@ -899,7 +901,6 @@ copy("cronet_package_copy") {
     "$root_out_dir/lib.java/components/cronet/android/cronet_api.jar",
     "//AUTHORS",
     "//chrome/VERSION",
-    "//components/cronet/android/proguard.cfg",
   ]
   outputs = [
     "$_package_dir/{{source_file_part}}",
@@ -910,6 +911,20 @@ copy("cronet_package_copy") {
   ]
 }
 
+action("cronet_combine_proguard_flags") {
+  script = "//components/cronet/tools/generate_proguard_file.py"
+  outputs = [
+    "$_package_dir/proguard.cfg",
+  ]
+
+  args = [
+    "--output-file",
+    rebase_path("$_package_dir/proguard.cfg", root_build_dir),
+    rebase_path("//base/android/base_proguard_config.flags", root_build_dir),
+    rebase_path("//components/cronet/android/proguard.cfg", root_build_dir),
+  ]
+}
+
 copy("cronet_package_copy_native_lib") {
   sources = [
     "$root_out_dir/libcronet.so",
@@ -936,6 +951,7 @@ copy("cronet_package_copy_native_lib_unstripped") {
 
 group("cronet_package") {
   deps = [
+    ":cronet_combine_proguard_flags",
     ":cronet_package_copy",
     ":cronet_package_copy_native_lib",
     ":cronet_package_copy_native_lib_unstripped",