app_list: set all apps indicator negative transition offset limit

changes:
Set all apps indicator negative transition offset limit to the place of
initial suggested apps indicator.
This will make:
(1) when scrolling up, all apps indicator will stop at 21px padding
away from search box, while all apps tiles scrolling underneath it.
(2) all apps indicator will be shown on non-first page due to (1).

Bug: 741009
TEST: tested with fullscreen app list enabled
Change-Id: I7fa71f041f81b0939c507fb246589cfdb6dbc06a
Reviewed-on: https://chromium-review.googlesource.com/569378Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Qiang(Joe) Xu <warx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486230}

ui/app_list/views/apps_grid_view.cc

@@ -896,7 +896,10 @@ void AppsGridView::LayoutAllAppsIndicator(gfx::Rect* rect) {
   indicator_rect.Inset((indicator_rect.width() - indicator_size.width()) / 2,
                        0);
   const gfx::Vector2d page_zero_offset = CalculateTransitionOffset(0);
-  indicator_rect.Offset(page_zero_offset.x(), page_zero_offset.y());
+  const int y_offset_limit = -kSuggestionsAllAppsIndicatorPadding -
+                             kGridTileHeight - indicator_size.height();
+  indicator_rect.Offset(page_zero_offset.x(),
+                        std::max(y_offset_limit, page_zero_offset.y()));
   all_apps_indicator_->SetBoundsRect(indicator_rect);
 }