This is not necessarily URL an string result.
Pasting on a UITextField will result by default in concatenating all available items.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b3825e6edb712e4128d74e45308749baa2d84e56

commit b3825e6edb712e4128d74e45308749baa2d84e56
Author: stkhapugin@chromium.org <stkhapugin@chromium.org>
Date: Wed Sep 06 09:44:07 2017

Omnibox paste delegate.

Introduce a paste delegate for omnibox on iOS 11 in order to avoid
repeated pastes of the copied URL.

Bug:  756855 
Change-Id: I78ff6d1bd6c4486446d7f7c9b32c3a1487152a65
Reviewed-on: https://chromium-review.googlesource.com/621306
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499919}
[modify] https://crrev.com/b3825e6edb712e4128d74e45308749baa2d84e56/ios/chrome/browser/ui/omnibox/BUILD.gn
[add] https://crrev.com/b3825e6edb712e4128d74e45308749baa2d84e56/ios/chrome/browser/ui/omnibox/omnibox_text_field_paste_delegate.h
[add] https://crrev.com/b3825e6edb712e4128d74e45308749baa2d84e56/ios/chrome/browser/ui/omnibox/omnibox_text_field_paste_delegate.mm
[modify] https://crrev.com/b3825e6edb712e4128d74e45308749baa2d84e56/ios/chrome/browser/ui/omnibox/omnibox_view_ios.h
[modify] https://crrev.com/b3825e6edb712e4128d74e45308749baa2d84e56/ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm

[Auto-generated comment by a script] We noticed that this issue is targeted for M-62; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-62 label, otherwise remove Merge-TBD label. Thanks.

I think per https://bugs.chromium.org/p/chromium/issues/detail?id=755620#c22 this needs to be cherry-picked. 

Verified on iOS 11 beta 9 on iPad Pro , iPhone 6+  on build 63.0.3213.0canary
Pasting into omnibox when the paste item consists of both URL and a string does NOT result in the pasted URL being repeated twice.

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

If all merges have been completed, please remove any remaining Merge-Approved labels from this issue.

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The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b

commit 4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b
Author: stkhapugin@chromium.org <stkhapugin@chromium.org>
Date: Mon Sep 18 16:49:01 2017

Omnibox paste delegate.

Introduce a paste delegate for omnibox on iOS 11 in order to avoid
repeated pastes of the copied URL.

Bug:  756855 
Change-Id: I78ff6d1bd6c4486446d7f7c9b32c3a1487152a65
Reviewed-on: https://chromium-review.googlesource.com/621306
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#499919}(cherry picked from commit b3825e6edb712e4128d74e45308749baa2d84e56)
Reviewed-on: https://chromium-review.googlesource.com/668616
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/branch-heads/3202@{#290}
Cr-Branched-From: fa6a5d87adff761bc16afc5498c3f5944c1daa68-refs/heads/master@{#499098}
[modify] https://crrev.com/4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b/ios/chrome/browser/ui/omnibox/BUILD.gn
[add] https://crrev.com/4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b/ios/chrome/browser/ui/omnibox/omnibox_text_field_paste_delegate.h
[add] https://crrev.com/4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b/ios/chrome/browser/ui/omnibox/omnibox_text_field_paste_delegate.mm
[modify] https://crrev.com/4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b/ios/chrome/browser/ui/omnibox/omnibox_view_ios.h
[modify] https://crrev.com/4a18e2ed4e588ac9c353bb5da3fec2dc27efc97b/ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm

Verified the issue on 62.0.3202.29 beta tested on iOS 11.0.
Pasting into omnibox when the paste item consists of both URL and a string does NOT result in the pasted URL being repeated twice,works fine.