build full 64bit WebView

android_webview/system_webview_apk_tmpl.gni

Index: android_webview/system_webview_apk_tmpl.gni
diff --git a/android_webview/system_webview_apk_tmpl.gni b/android_webview/system_webview_apk_tmpl.gni
index 828263e2b84ddcb54928e4d4a2d63e92a3ac7cf6..6b19945bbf4fdccb8353e0c879a697ac00411692 100644
--- a/android_webview/system_webview_apk_tmpl.gni
+++ b/android_webview/system_webview_apk_tmpl.gni
@@ -25,6 +25,9 @@ template("system_webview_apk_tmpl") {
         rebase_path("$root_gen_dir/CHROME_VERSION.json", root_out_dir)
     native_lib_version_arg = "@FileArg($_native_lib_file:full-quoted)"
     extensions_to_not_compress = ".lpak,.pak,.bin,.dat"
+    if (build_apk_secondary_abi && android_64bit_target_cpu) {
+      secondary_abi_shared_libraries = [ "//android_webview:libwebviewchromium($android_secondary_abi_toolchain)" ]
+    }
 
     if (!is_java_debug) {
       proguard_enabled = true