Use the URL passed to navigator.share().

third_party/WebKit/public/BUILD.gn

 # Copyright 2014 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("//mojo/public/tools/bindings/mojom.gni")
 import("//third_party/WebKit/Source/config.gni")
 import("//tools/grit/grit_rule.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
@@ skipping 686 matching lines @@
   export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
   export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
 }
 
 # GYP version: WebKit/public/blink.gyp:android_mojo_bindings_java
 mojom("android_mojo_bindings") {
   sources = [
     "platform/modules/payments/payment_request.mojom",
     "platform/modules/webshare/webshare.mojom",
   ]
+  public_deps = [
+    "//url/mojo:url_mojom_gurl",
+  ]
 
   use_new_wrapper_types = false
 
   # See comment above.
   export_class_attribute = "CONTENT_EXPORT"
   export_define = "CONTENT_IMPLEMENTATION=1"
   export_header = "content/common/content_export.h"
   export_class_attribute_blink = "BLINK_PLATFORM_EXPORT"
   export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
   export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
@@ skipping 18 matching lines @@
   export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
   export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
 }
 
 group("generate_mojo_bindings") {
   deps = [
     ":mojo_bindings_blink__generator",
     ":offscreen_canvas_mojo_bindings_blink__generator",
   ]
 }