Fix DCHECK when entering fullscreen on Linux with the GTK theme

Also fixes a logic error in opaque_browser_frame_view_layout.cc introduced by
e831694a.

BUG=882854,887598
R=pkasting
CC=​iclelland

Change-Id: I5b1b6eb4d737ecbed3102d046b06cacdef7cddaa
Reviewed-on: https://chromium-review.googlesource.com/1236267
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593041}

chrome/browser/ui/libgtkui/nav_button_provider_gtk.cc

@@ -210,6 +210,9 @@ class NavButtonImageSource : public gfx::ImageSkiaSource {
     // RenderNavButton() is called at most once for each needed scale
     // factor.  Additionally, buttons in the HOVERED or PRESSED states
     // are not actually rendered until they are needed.
+    if (button_size_.IsEmpty())
+      return gfx::ImageSkiaRep();
+
     auto button_context = AppendCssNodeToStyleContext(
         CreateHeaderContext(maximized_), "GtkButton#button.titlebutton");
     gtk_style_context_add_class(button_context,

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

@@ -191,7 +191,7 @@ int OpaqueBrowserFrameViewLayout::NonClientTopHeight(bool restored) const {
 
 int OpaqueBrowserFrameViewLayout::GetTabStripInsetsTop(bool restored) const {
   const int top = NonClientTopHeight(restored);
-  return !restored || !delegate_->IsFrameCondensed()
+  return !restored && delegate_->IsFrameCondensed()
              ? top
              : (top + GetNonClientRestoredExtraThickness());
 }