Fix single tab mode damage being incorrect after uninstalling a theme.

When BrowserNonClientFrameView is destroyed and recreated, for example
when the user installs or uninstalls a theme, the BrowserView is reused.
But the Tabstrip was only being observed on BrowserView creation.

This is probably a very old bug, but it's hard to observe the effects
without single tab mode. In particular, I found that the profile
switcher chip can get out of sync with the size of the tabstrip and
overlap the new tab button, which is also fixed.

Bug: 841643
Change-Id: Ia3c20a70f8082e1a8b90d34da35011313c344035
Reviewed-on: https://chromium-review.googlesource.com/1079958Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563080}

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

@@ -52,6 +52,7 @@ BrowserNonClientFrameView::BrowserNonClientFrameView(BrowserFrame* frame,
     g_browser_process->profile_manager()->
         GetProfileAttributesStorage().AddObserver(this);
   }
+  MaybeObserveTabstrip();
 }
 
 BrowserNonClientFrameView::~BrowserNonClientFrameView() {
@@ -68,10 +69,7 @@ int BrowserNonClientFrameView::GetAvatarIconPadding() {
 }
 
 void BrowserNonClientFrameView::OnBrowserViewInitViewsComplete() {
-  if (browser_view()->tabstrip()) {
-    DCHECK(!tab_strip_observer_.IsObserving(browser_view()->tabstrip()));
-    tab_strip_observer_.Add(browser_view()->tabstrip());
-  }
+  MaybeObserveTabstrip();
   UpdateMinimumSize();
 }
 
@@ -422,6 +420,13 @@ void BrowserNonClientFrameView::OnProfileHighResAvatarLoaded(
   UpdateTaskbarDecoration();
 }
 
+void BrowserNonClientFrameView::MaybeObserveTabstrip() {
+  if (browser_view()->tabstrip()) {
+    DCHECK(!tab_strip_observer_.IsObserving(browser_view()->tabstrip()));
+    tab_strip_observer_.Add(browser_view()->tabstrip());
+  }
+}
+
 const ui::ThemeProvider*
 BrowserNonClientFrameView::GetThemeProviderForProfile() const {
   // Because the frame's accessor reads the ThemeProvider from the profile and

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

@@ -149,6 +149,8 @@ class BrowserNonClientFrameView : public views::NonClientFrameView,
   void OnProfileHighResAvatarLoaded(
       const base::FilePath& profile_path) override;
 
+  void MaybeObserveTabstrip();
+
   // Gets a theme provider that should be non-null even before we're added to a
   // view hierarchy.
   const ui::ThemeProvider* GetThemeProviderForProfile() const;