Rename enable_arcore jinja variable to include_arcore_manifest_flag

This flag will be set appropriately depending on the context for
which the manifest is generated (bundle vs APK).

This CL maintains current behavior.

Change-Id: I543e09d07e2bea4769e2d4a71663b10b140c01c6
Reviewed-on: https://chromium-review.googlesource.com/c/1394864
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619743}

chrome/android/chrome_public_apk_tmpl.gni

@@ -31,8 +31,8 @@ declare_args() {
 
 default_chrome_public_jinja_variables = [
   "channel=$android_channel",
-  "enable_arcore=$enable_arcore",
   "enable_vr=$enable_vr",
+  "include_arcore_manifest_flag=$enable_arcore",
 ]
 
 if (android_64bit_browser) {

chrome/android/java/AndroidManifest.xml

@@ -165,7 +165,7 @@ by a child template that "extends" this file.
         <meta-data android:name="android.content.APP_RESTRICTIONS"
             android:resource="@xml/app_restrictions"/>
 
-        {% if enable_arcore %}
+        {% if include_arcore_manifest_flag == 'true' %}
         <!-- ARCore APK integration -->
         <!-- This tag indicates that this application optionally uses ARCore. -->
         <meta-data android:name="com.google.ar.core" android:value="optional" />