build full 64bit WebView

android_webview/system_webview_apk_tmpl.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 
 template("system_webview_apk_tmpl") {
   android_apk(target_name) {
     forward_variables_from(invoker, "*")
 
     deps += [
       "//android_webview:assets",
       "//base:base_java",
     ]
 
     if (!defined(alternative_android_sdk_jar)) {
       alternative_android_sdk_jar = webview_framework_jar
     }
 
     shared_resources = true
     shared_libraries = [ "//android_webview:libwebviewchromium" ]
     native_lib_version_rule = "//build/util:chrome_version_json"
     _native_lib_file =
         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 ((!defined(merge_64bit_webview) || !merge_64bit_webview) &&

[Torne, 2016/09/12 12:43:42]

Am I interepreting this correctly that setting merge_64bit_webview=true makes it
build a WebView that's *only* 64-bit, suitable for later manual merging?

If so that seems like a really unintuitive name for that variable - without any
context I would have assumed that merge_64bit_webview=true is what I wanted to
build a merged APK with both architectures.

So unless I have this backwards, I'd suggest we rename this variable to
something else. Something like "webview_64bit_only"? The merging doesn't seem to
really be relevant - it's just about building a 64-bit only APK, no?

Also:
1) What's the default behaviour going to be when you just build WebView without
specifying any config?
2) How is this going to impact Monochrome? What's the default behaviour there,
and how do we control it?

[michaelbai, 2016/09/12 19:41:13]

It seemed merge_64bit_webview is not a good name, sure, I changed it to
webview_64bit_only. 

Yes, it should be webview_64bit_only, just find out my branch name for this
patch is webview_64bit_only :).
It will build full 64-bit WebView APK which has both 32-bit and 64-bit binaries.
Monochrome will use same variable webview_64bit_only, the default behavior is
same as WebView, if webview_64bit_only is not true, Monochrome apk will have
both 32-bit and 64-bit binaries.

See downstream patch: 
https://chrome-internal-review.googlesource.com/285815

The places where it turns on are release bot and build bot to protect this
configuration.

+        android_64bit_target_cpu) {
+      secondary_abi_shared_libraries =
+          [ "//android_webview:webviewchromium_secondary_abi_lib" ]
+    }
+
     if (!is_java_debug) {
       proguard_enabled = true
       if (!defined(proguard_configs)) {
         proguard_configs = []
       }
       proguard_configs += [
         "//android_webview/apk/java/proguard.flags",
         "//base/android/base_proguard_config.flags",
         "//base/android/release_proguard_config.flags",
       ]
     }
   }
 }