Don't use the "glass" opacities in the tabstrip when the window is opaque.

This can't be done by mucking with ShouldWindowContentsBeTransparent() as I
opriginally thought; update comment there to describe better why.

Instead, do this directly in TabStripImpl.

The net effect of this should be that on Win 10, the titlebar background color
will no longer show through the background tabs in the default theme; for white
titlebars, this should make active and inactive tabs a little easier to
distinguish.

BUG=none
TEST=none

Change-Id: I1b722ba7ce887a1a32470e794e04b436bc06c22b
Reviewed-on: https://chromium-review.googlesource.com/802522Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521075}

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

@@ -72,6 +72,7 @@
 #include "ui/views/window/non_client_view.h"
 
 #if defined(OS_WIN)
+#include "base/win/windows_version.h"
 #include "ui/display/win/screen_win.h"
 #include "ui/gfx/win/hwnd_util.h"
 #include "ui/views/win/hwnd_util.h"
@@ -725,7 +726,7 @@ SkAlpha TabStripImpl::GetInactiveAlpha(bool for_new_tab_button) const {
 #else
   static const SkAlpha kInactiveTabAlphaGlass = 200;
   static const SkAlpha kInactiveTabAlphaOpaque = 255;
-  const SkAlpha base_alpha = GetWidget()->ShouldWindowContentsBeTransparent()
+  const SkAlpha base_alpha = TitlebarBackgroundIsTransparent()
                                  ? kInactiveTabAlphaGlass
                                  : kInactiveTabAlphaOpaque;
 #endif  // OS_CHROMEOS
@@ -1020,7 +1021,7 @@ base::string16 TabStripImpl::GetAccessibleTabName(const Tab* tab) const {
 int TabStripImpl::GetBackgroundResourceId(bool* custom_image) const {
   const ui::ThemeProvider* tp = GetThemeProvider();
 
-  if (GetWidget()->ShouldWindowContentsBeTransparent()) {
+  if (TitlebarBackgroundIsTransparent()) {
     const int kBackgroundIdGlass = IDR_THEME_TAB_BACKGROUND_V;
     *custom_image = tp->HasCustomImage(kBackgroundIdGlass);
     return kBackgroundIdGlass;
@@ -1411,6 +1412,16 @@ bool TabStripImpl::ShouldHighlightCloseButtonAfterRemove() {
   return in_tab_close_;
 }
 
+bool TabStripImpl::TitlebarBackgroundIsTransparent() const {
+#if defined(OS_WIN)
+  // Windows 8+ uses transparent window contents (because the titlebar area is
+  // drawn by the system and not Chrome), but the actual titlebar is opaque.
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8)
+    return false;
+#endif
+  return GetWidget()->ShouldWindowContentsBeTransparent();
+}
+
 void TabStripImpl::DoLayout() {
   last_layout_size_ = size();
 

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

@@ -316,6 +316,9 @@ class TabStripImpl : public TabStrip,
   // Returns whether the highlight button should be highlighted after a remove.
   bool ShouldHighlightCloseButtonAfterRemove();
 
+  // Returns whether the window background behind the tabstrip is transparent.
+  bool TitlebarBackgroundIsTransparent() const;
+
   // Invoked from Layout if the size changes or layout is really needed.
   void DoLayout();
 

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

@@ -413,10 +413,12 @@ bool DesktopWindowTreeHostWin::ShouldUseNativeFrame() const {
 }
 
 bool DesktopWindowTreeHostWin::ShouldWindowContentsBeTransparent() const {
-  // If the window has a native frame, we assume it is an Aero Glass window, and
-  // is therefore transparent. Note: This is not equivalent to calling
-  // IsAeroGlassEnabled, because ShouldUseNativeFrame is overridden in a
-  // subclass.
+  // The window contents need to be transparent when the titlebar area is drawn
+  // by the DWM rather than Chrome, so that area can show through.  This
+  // function does not describe the transparency of the whole window appearance,
+  // but merely of the content Chrome draws, so even when the system titlebars
+  // appear opaque (Win 8+), the content above them needs to be transparent, or
+  // they'll be covered by a black (undrawn) region.
   return ShouldUseNativeFrame() && !IsFullscreen();
 }