Update WebAPK if homescreen icon changed.

chrome/android/webapk/shell_apk/BUILD.gn

 # 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/rules.gni")
 
 declare_args() {
   # The origin URL of the WebAPK. Used to generate a unique package name for
   # WebAPK. Example: "foo.com"
   webapk_manifest_package_origin = "template"
@@ skipping 10 matching lines @@
   webapk_short_name = "Sample WebAPK"
   webapk_scope_url = "https://www.template.com"
   webapk_display_mode = "standalone"
   webapk_orientation = "portrait"
   webapk_theme_color = "2147483648L"  # HostBrowserLauncher#MANIFEST_COLOR_INVALID_OR_MISSING
   webapk_background_color = "2147483648L"  #HostBrowserLauncher#MANIFEST_COLOR_INVALID_OR_MISSING
 
   # The URL of the app icon. Empty if the app icon is generated.
   webapk_icon_url = "http://www.template.com/icon.png"
 
+  # Murmur2 hash of the homescreen icon. The hash should be of the icon as it is
+  # available from the web. The icon bytes should not be transformed (e.g.
+  # decoding / encoding) prior to taking the hash.
+  webapk_icon_murmur2_hash = "0L"
+
   # Host part of |webapk_scope_url|.
   webapk_scope_url_host = "www.template.com"
 }
 
 shell_apk_manifest_package =
     "org.chromium.webapk.$webapk_manifest_package_origin"
 
 shell_apk_manifest = "$target_gen_dir/shell_apk_manifest/AndroidManifest.xml"
 
 jinja_template("shell_apk_manifest") {
   input = "AndroidManifest.xml"
   output = shell_apk_manifest
 
   variables = [
     "manifest_package=$shell_apk_manifest_package",
     "runtime_host=$webapk_runtime_host",
     "start_url=$webapk_start_url",
     "name=$webapk_name",
     "short_name=$webapk_short_name",
     "scope_url=$webapk_scope_url",
     "display_mode=$webapk_display_mode",
     "orientation=$webapk_orientation",
     "theme_color=$webapk_theme_color",
     "background_color=$webapk_background_color",
     "icon_url=$webapk_icon_url",
+    "icon_murmur2_hash=$webapk_icon_murmur2_hash",
     "scope_url_host=$webapk_scope_url_host",
     "web_manifest_url=$webapk_web_manifest_url",
   ]
 }
 
 android_resources("shell_apk_resources") {
   resource_dirs = [ "res" ]
   custom_package = "org.chromium.webapk.shell_apk"
 }
 
@@ skipping 50 matching lines @@
 }
 
 junit_binary("webapk_shell_apk_junit_tests") {
   java_files = [ "junit/src/org/chromium/webapk/shell_apk/HostBrowserClassLoaderTest.java" ]
   deps = [
     ":webapk_java",
     "//base:base_junit_test_support",
     "//chrome/android/webapk/libs/common:common_java",
   ]
 }