Don't close tabstrip on resize in ChromeOS

See attached bug.

Bug: 1135317
Change-Id: I4a60b5266b20e246bea14e9330fa41c8a743091d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2458747Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814923}

chrome/browser/ui/views/frame/webui_tab_strip_container_view.cc

@@ -236,9 +236,12 @@ class WebUITabStripContainerView::AutoCloser : public ui::EventHandler,
     DCHECK(top_container_);
     DCHECK(content_area_);
     DCHECK(omnibox_);
-    view_observer_.Add(top_container_);
+
     view_observer_.Add(content_area_);
     view_observer_.Add(omnibox_);
+#if defined(OS_WIN)
+    view_observer_.Add(top_container_);
+#endif  // defined(OS_WIN)
 
     // Our observed Widget's NativeView may be destroyed before us. We
     // have no reasonable way of un-registering our pre-target handler
@@ -828,6 +831,7 @@ gfx::Size WebUITabStripContainerView::FlexRule(
 }
 
 void WebUITabStripContainerView::OnViewBoundsChanged(View* observed_view) {
+#if defined(OS_WIN)
   if (observed_view == top_container_) {
     if (old_top_container_width_ != top_container_->width()) {
       old_top_container_width_ = top_container_->width();
@@ -835,7 +839,11 @@ void WebUITabStripContainerView::OnViewBoundsChanged(View* observed_view) {
       drag_to_open_handler_->CancelDrag();
       CloseContainer();
     }
-  } else if (observed_view == tab_contents_container_) {
+    return;
+  }
+#endif  // defined(OS_WIN)
+
+  if (observed_view == tab_contents_container_) {
     // TODO(pbos): PreferredSizeChanged seems to cause infinite recursion with
     // BrowserView::ChildPreferredSizeChanged. InvalidateLayout here should be
     // replaceable with PreferredSizeChanged.

chrome/browser/ui/views/frame/webui_tab_strip_container_view.h

@@ -11,6 +11,7 @@
 #include "base/optional.h"
 #include "base/scoped_observer.h"
 #include "base/time/time.h"
+#include "build/build_config.h"
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui.h"
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui_embedder.h"
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui_metrics.h"
@@ -139,10 +140,16 @@ class WebUITabStripContainerView : public TabStripUIEmbedder,
   views::View* tab_contents_container_;
   views::View* tab_counter_ = nullptr;
 
+#if defined(OS_WIN)
   // If the user interacts with Windows in a way that changes the width of the
   // window, close the top container. This is similar to the auto-close when the
   // user touches outside the tabstrip.
+  //
+  // TODO(dfried, davidbienvenu): we can remove this as soon as we move to the
+  // more modern Windows drag-drop system, avoiding some of the weirdness around
+  // starting drag-drop.
   int old_top_container_width_ = 0;
+#endif  // defined(OS_WIN)
 
   base::Optional<float> current_drag_height_;