[iOS] Reset content inset when overscroll action is cancelled.

This CL updates OverscrollActionsController to reset the scroll view's
top content inset when the gesture is cancelled.  This occurs before
reenabling the FullscreenController, as the content inset is used to
check whether the page's rendered content fits in the current viewport.
If the content fits, then scrolls will be ignored.

TBR=kkhorimoto@chromium.org

(cherry picked from commit b4e1a9ae423022a5bb87a9250d933fb5e1057427)

Bug: 809853, 809856
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I60c58b8ec75ae126217a58be2f3792048fc27e5c
Reviewed-on: https://chromium-review.googlesource.com/912272
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#536174}
Reviewed-on: https://chromium-review.googlesource.com/932549
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#556}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
diff --git a/ios/chrome/browser/ui/overscroll_actions/overscroll_actions_controller.mm b/ios/chrome/browser/ui/overscroll_actions/overscroll_actions_controller.mm
index 10dadb7..0b568be 100644
--- a/ios/chrome/browser/ui/overscroll_actions/overscroll_actions_controller.mm
+++ b/ios/chrome/browser/ui/overscroll_actions/overscroll_actions_controller.mm
@@ -742,6 +742,7 @@
       [[NSNotificationCenter defaultCenter]
           postNotificationName:kOverscrollActionsDidEnd
                         object:self];
+      [self resetScrollViewTopContentInset];
       _fullscreenDisabler = nullptr;
       if (_shouldInvalidate) {
         [self invalidate];