Greatly simplify tabstrip available width calculation.

Previously, this calculation used LayoutManager::GetAvailableSize,
which relied on cached information that was cleared during layout.
An extra layout was added to fill this cache, which caused no end
of complexities in tabstrip layout.

This is totally unnecessary, as all of the siblings of TabStrip
are simple fixed-width controls - NTB, grab handle, tab search
button, and scroll controls. A wee bit of arithmetic suffices.

Bug: 1093972
Change-Id: I7758bd80ba37b31d5efeeafd208e093094ef5e17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2426978Reviewed-by: Connie Wan <connily@chromium.org>
Reviewed-by: Charlene Yan <cyan@chromium.org>
Commit-Queue: Charlene Yan <cyan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810541}

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

@@ -92,7 +92,7 @@ bool TabStripRegionView::IsRectInWindowCaption(const gfx::Rect& rect) {
   // Check to see if the rect intersects the non-button parts of the tab search
   // button. The enclosed button has a non-rectangular shape, so if it's not in
   // the visual portions of the buttons we treat it as a click to the caption.
-  if (tab_search_button_->GetLocalBounds().Intersects(
+  if (tab_search_button_ && tab_search_button_->GetLocalBounds().Intersects(
                                 get_target_rect(tab_search_button_))) {
     return !tab_search_button_->HitTestRect(
         get_target_rect(tab_search_button_));
@@ -136,12 +136,13 @@ void TabStripRegionView::OnThemeChanged() {
 }
 
 int TabStripRegionView::CalculateTabStripAvailableWidth() {
-  Layout();
-  views::SizeBound available_width =
-      GetAvailableSize(tab_strip_container_).width();
-  // |available_width| might still be unbounded in cases where the tabstrip is
-  // hidden (e.g. presentation mode on MacOS). In these cases we don't care
-  // about the resulting layout, since the tabstrip is not visible, so we can
-  // substitute 0 to ensure that we relayout once the width is defined again.
-  return available_width.is_bounded() ? available_width.value() : 0;
+  // The tab strip can occupy the space not currently taken by its fixed-width
+  // sibling views.
+  int reserved_width = 0;
+  for (View* const child : children()) {
+    if (child != tab_strip_container_)
+      reserved_width += child->size().width();
+  }
+
+  return size().width() - reserved_width;
 }

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -2200,10 +2200,6 @@ SkColor TabStrip::GetPaintedGroupColor(
 // TabStrip, views::AccessiblePaneView overrides:
 
 void TabStrip::Layout() {
-  if (is_doing_layout_)
-    return;
-  base::AutoReset<bool> layout_guard(&is_doing_layout_, true);
-
   if (IsAnimating()) {
     // Hide tabs that have animated at least partially out of the clip region.
     SetTabSlotVisibility();

chrome/browser/ui/views/tabs/tab_strip.h

@@ -747,9 +747,6 @@ class TabStrip : public views::AccessiblePaneView,
   // The width available for tabs at the time of last layout.
   int last_available_width_ = 0;
 
-  // Guard to protect against layout loops.
-  bool is_doing_layout_ = false;
-
   // See description above stacked_layout().
   bool stacked_layout_ = false;