GMC: Fix crash when updating icon

This CL modifies the MediaToolbarButtonView to check for a Widget
before updating its icons. This prevents a crash where the button would
try to read theme data from the Widget after it was gone. In addition,
this CL changes the logic for updating the icon on enable/disable to
only happen on Mac, since Mac is the only OS where the icon can change
from enabling/disabling.

Bug: 1006359
Change-Id: I009d5e5e921982be2628ce51f0488c463985dd58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815904Reviewed-by: Jazz Xu <jazzhsu@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699062}

chrome/browser/ui/views/global_media_controls/media_toolbar_button_view.cc

@@ -68,14 +68,18 @@ void MediaToolbarButtonView::Hide() {
 
 void MediaToolbarButtonView::Enable() {
   SetEnabled(true);
-  UpdateIcon();
   InformIPHOfButtonEnabled();
+#if defined(OS_MACOSX)
+  UpdateIcon();
+#endif  // defined(OS_MACOSX)
 }
 
 void MediaToolbarButtonView::Disable() {
   SetEnabled(false);
-  UpdateIcon();
   InformIPHOfButtonDisabledorHidden();
+#if defined(OS_MACOSX)
+  UpdateIcon();
+#endif  // defined(OS_MACOSX)
 }
 
 SkColor MediaToolbarButtonView::GetInkDropBaseColor() const {
@@ -85,6 +89,9 @@ SkColor MediaToolbarButtonView::GetInkDropBaseColor() const {
 }
 
 void MediaToolbarButtonView::UpdateIcon() {
+  if (!GetWidget())
+    return;
+
   const gfx::VectorIcon& icon = ::vector_icons::kQueueMusicIcon;
 
   const SkColor normal_color =