Update extensions button's color when overriding icon color

In the previous CL, a code calling ExtensionToolbarButton::UpdateIcon()
from ExtensionToolbarContainer was removed.
(https://chromium-review.googlesource.com/c/chromium/src/+/2253600/29/chrome/browser/ui/views/extensions/extensions_toolbar_container.cc)

However, ExtensionToolbarButton should update icon color
when WebAppFrameToolbar overrides icon color for ExtensionToolbarButton.
(https://chromium.googlesource.com/chromium/src/+/master/chrome/browser/ui/views/web_apps/web_app_frame_toolbar_view.cc#471)
Otherwise, ExtensionToolbarButton ignores the overridden color.

When WebAppFrameToolbar overrides icon color, ExtensionToolbarContainer::UpdateAllIcon()
we be called. Thus, we should call ExtensionToolbarButton::UpdateIcon() in it.

Bug: 1106698, 1048901
Change-Id: I2082a16d18b312cd5a578f2c84b709e60cee6c5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303418Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789552}

chrome/browser/ui/views/extensions/extensions_toolbar_container.cc

@@ -105,6 +105,7 @@ ExtensionsToolbarContainer::~ExtensionsToolbarContainer() {
 }
 
 void ExtensionsToolbarContainer::UpdateAllIcons() {
+  extensions_button_->UpdateIcon();
   for (const auto& action : actions_)
     action->UpdateState();
 }