Fix frame buttons rendering too large when using OSX-Arc-White GTK theme

The check for GTK 3.20 was incorrect as the issue it was trying to fix
was still occurring on GTK 3.20+ systems.  This CL adds the correct,
but more complex, check.

Verified on these configurations:
{GTK 3.18, GTK 3.22} X
{Breeze, Adwaita, OSX-Arc-White, Greybird} X
{scale=1, scale=2} X
{fullscreen, restored}

BUG=821881
R=thestig

Change-Id: I05afa35c1452a46a1abf4c39191a13657bfd8e2c
Reviewed-on: https://chromium-review.googlesource.com/990717Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547921}

chrome/browser/ui/libgtkui/nav_button_provider_gtk3.cc

@@ -213,7 +213,23 @@ class NavButtonImageSource : public gfx::ImageSkiaSource {
     // is not scaled for the (unexpected) smaller button size, and the button's
     // edges appear cut off.  To fix this, manually set the background to scale
     // to the button size when it would have clipped.
-    if (GtkVersionCheck(3, 20)) {
+    //
+    // GTK's "contain" is unlike CSS's "contain".  In CSS, the image would only
+    // be downsized when it would have clipped.  In GTK, the image is always
+    // scaled to fit the drawing region (preserving aspect ratio).  Only add
+    // "contain" if clipping would occur.
+    cairo_pattern_t* cr_pattern = nullptr;
+    cairo_surface_t* cr_surface = nullptr;
+    gtk_style_context_get(button_context, button_state,
+                          GTK_STYLE_PROPERTY_BACKGROUND_IMAGE, &cr_pattern,
+                          nullptr);
+    if (cr_pattern &&
+        cairo_pattern_get_surface(cr_pattern, &cr_surface) ==
+            CAIRO_STATUS_SUCCESS &&
+        cr_surface &&
+        cairo_surface_get_type(cr_surface) == CAIRO_SURFACE_TYPE_IMAGE &&
+        (cairo_image_surface_get_width(cr_surface) > button_size_.width() ||
+         cairo_image_surface_get_height(cr_surface) > button_size_.height())) {
       ApplyCssToContext(button_context,
                         ".titlebutton { background-size: contain; }");
     }