Speculative fix for crash during browser startup with opaque frame.

Unconditionally requesting the browser's toolbar view causes a null deref.  Try
to guard by checking if the toolbar is visible first.  This should fix the crash
unless at this point the toolbar feature is turned on but the toolbar view
itself has not been created.  Hopefully that's not the case.

BUG=581673
TEST=none
TBR=sky

Review URL: https://codereview.chromium.org/1649493003

Cr-Commit-Position: refs/heads/master@{#371970}

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

@@ -387,7 +387,7 @@ void OpaqueBrowserFrameViewLayout::LayoutIncognitoIcon(views::View* host) {
   int min_button_width = NonClientBorderThickness();
   // In non-MD, the toolbar has a rounded corner that we don't want the tabstrip
   // to overlap.
-  if (!md && !avatar_button_)
+  if (!md && !avatar_button_ && delegate_->IsToolbarVisible())
     min_button_width += delegate_->GetToolbarLeadingCornerClientWidth();
   leading_button_start_ = std::max(leading_button_start_, min_button_width);
   // The trailing corner is a mirror of the leading one.