Android: Specify monochrome unwind asset in public repo

When bundles start using bundle-specific native libraries, the unwind
asset name will need to change accordingly.  This is easier to do if the
asset name is specified alongside the native library, which currently
isn't always the case.  Monochrome specifies its shared library in the
public repo, but names the unwind asset in the internal repo.  That
means there'll be a build break if the library changes names.

Note that non-Monochrome doesn't have this problem, because its public
and internal configurations both specify the library and asset names
together.  These templates also don't have the luxury of specifying such
properties in a root template, because they're reused by test APKs.

We can clean this up with the following sequence:

1. Add the "monochrome" unwind asset specifier in the public repo.  This
will duplicate the value currently set in the internal repo.

2. Remove the internal repo variable assignment.

3. Land the bundle-specific libraries with their new names.

BUG=874584

Change-Id: I7f4db40c0496a7f17e766afb1ba7e2b290054551
Reviewed-on: https://chromium-review.googlesource.com/c/1346809Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610163}

chrome/android/BUILD.gn

@@ -1558,9 +1558,6 @@ template("monochrome_public_apk_or_module_tmpl") {
     add_unwind_tables_in_apk =
         _add_unwind_tables_in_chrome_public_apk &&
         (!defined(use_trichrome_library) || !use_trichrome_library)
-    if (add_unwind_tables_in_apk && can_unwind_with_cfi_table) {
-      shared_library_for_unwind_asset = "monochrome"
-    }
 
     version_name = chrome_version_name
     if (experimental_r8_path == "") {

chrome/android/chrome_public_apk_tmpl.gni

@@ -228,6 +228,9 @@ template("monochrome_public_common_apk_or_module_tmpl") {
         native_lib_placeholders = [ "libdummy.so" ]
       }
     }
+    if (invoker.add_unwind_tables_in_apk) {
+      shared_library_for_unwind_asset = "monochrome"
+    }
 
     alternative_android_sdk_dep = webview_framework_dep
     app_as_shared_lib = true