[omnibox] Move Header chevron from right side to directly adjacent

Previously, the header expand/collapse chevron button was on the far
right side of the header row.

This looked like a bug sometimes, when the header started out collapsed.

This CL moves the button to be directly adjacent to the header text.

See the bug for details.

Bug: 1127090
Change-Id: I23eba83d9ff58d31e6983af195fb219e668e9cbd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404663Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805971}

chrome/browser/ui/views/omnibox/omnibox_row_view.cc

@@ -44,10 +44,12 @@ class OmniboxRowView::HeaderView : public views::View,
     views::BoxLayout* layout =
         SetLayoutManager(std::make_unique<views::BoxLayout>(
             views::BoxLayout::Orientation::kHorizontal));
+    // The icons in the header view match their sizing to the location bar.
+    layout->set_between_child_spacing(
+        GetLayoutConstant(LOCATION_BAR_CHILD_INTERIOR_PADDING));
 
     header_label_ = AddChildView(std::make_unique<views::Label>());
     header_label_->SetHorizontalAlignment(gfx::HorizontalAlignment::ALIGN_LEFT);
-    layout->SetFlexForView(header_label_, 1);
 
     const gfx::FontList& font =
         views::style::GetFont(CONTEXT_OMNIBOX_PRIMARY,