Add GN arg "enable_proguard_obfuscation"

chrome/android/java/proguard-dont-obfuscate.flags

Index: chrome/android/java/proguard-dont-obfuscate.flags
diff --git a/build/linux/unbundle/libwebp.gn b/chrome/android/java/proguard-dont-obfuscate.flags
similarity index 54%
copy from build/linux/unbundle/libwebp.gn
copy to chrome/android/java/proguard-dont-obfuscate.flags
index 217911167b95466b4a64790f4cff7449da4a7253..b410239eabbc6adc8739695e0f52d42fde2f9681 100644
--- a/build/linux/unbundle/libwebp.gn
+++ b/chrome/android/java/proguard-dont-obfuscate.flags
@@ -2,9 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("libwebp") {
-  libs = [
-    "webp",
-    "webpdemux",
-  ]
+# Disables obfuscation for chromium packages.
+-keepnames,allowoptimization class com.google.android.apps.chrome.**,org.chromium.** {
+  *;
 }