Build libmonochrome.so with secondary toolchain

chrome/android/BUILD.gn

Index: chrome/android/BUILD.gn
diff --git a/chrome/android/BUILD.gn b/chrome/android/BUILD.gn
index 1e7eaa8f9a8f302df015238c7aff8a4750273853..de506b7a20b5479b258aba4748b4b159d44bf4bb 100644
--- a/chrome/android/BUILD.gn
+++ b/chrome/android/BUILD.gn
@@ -454,7 +454,14 @@ shared_library("chrome") {
 }
 
 # GYP: none
-if (!defined(webview_only_libmonochrome) || !webview_only_libmonochrome) {
+#
+# Only 32-bit //chrome/android/monochrome is needed, beside
+# being built with 32-bit default toolchain, it is also built
+# with secondary 32-bit toolchain in 64-bit platform because we
+# need 64-bit //android_webview/monochrome and 32-bit this target
+# for 64-bit APK.
+if (!android_64bit_target_cpu ||
+    current_toolchain == android_secondary_abi_toolchain) {
   shared_library("monochrome") {
     sources = chrome_apk_gypi.monochrome_app_native_sources
     deps = [
@@ -469,6 +476,12 @@ if (!defined(webview_only_libmonochrome) || !webview_only_libmonochrome) {
 
     public_configs = extra_chrome_shared_library_configs
   }
+} else {
+  group("monochrome_secondary_abi_lib") {
+    public_deps = [
+      ":monochrome($android_secondary_abi_toolchain)",
+    ]
+  }
 }
 
 # GYP: //chrome/android/chrome_apk.gyp:libchrome_sync_shell