Enable multidex for ChromePublic.apk.

chrome/android/chrome_public_apk_tmpl.gni

Index: chrome/android/chrome_public_apk_tmpl.gni
diff --git a/chrome/android/chrome_public_apk_tmpl.gni b/chrome/android/chrome_public_apk_tmpl.gni
index 5c98830dc8f0a79d248db8bab150f8ccafa4c173..a9347beb90f47837c59b866c613106cf7a94343f 100644
--- a/chrome/android/chrome_public_apk_tmpl.gni
+++ b/chrome/android/chrome_public_apk_tmpl.gni
@@ -41,14 +41,14 @@ template("chrome_public_apk_tmpl") {
         rebase_path("$root_gen_dir/CHROME_VERSION.json", root_out_dir)
     native_lib_version_arg = "@FileArg($_native_lib_file:full-quoted)"
 
-    if (is_java_debug) {
-      enable_multidex = true
-    } else {
+    enable_multidex = true
+    if (!is_java_debug) {
       proguard_enabled = true
       if (!defined(proguard_configs)) {
         proguard_configs = []
       }
       proguard_configs += [
+        "//build/android/main_dex_classes.flags",
         "//chrome/android/java/proguard.flags",
         "//base/android/proguard/chromium_apk.flags",
         "//base/android/proguard/chromium_code.flags",