[ToolbarMVC] Initialize theme color when ThemeColorProvider is first set

When lazily inflating the MenuButton, the call to setThemeColorProvider
doesn't trigger an immediate update, risking starting with the wrong
color/useLight combination if inflation occurs in a context where the
defaults aren't correct, e.g. incognito. This CL corrects the issue by
initializing the color immediately.

The need for this code should, however,
go away once the color is read from the model instead of directly, since
the initial bind will take care of problems like this.

Bug: 1127826
Change-Id: I609f42427a0b8fa877f4c165e97372d34047f28f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410590Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Patrick Noland <pnoland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807051}

chrome/android/java/src/org/chromium/chrome/browser/toolbar/menu_button/MenuButton.java

@@ -298,6 +298,7 @@ public class MenuButton extends FrameLayout implements TintObserver {
     public void setThemeColorProvider(ThemeColorProvider themeColorProvider) {
         mThemeColorProvider = themeColorProvider;
         mThemeColorProvider.addTintObserver(this);
+        onTintChanged(themeColorProvider.getTint(), themeColorProvider.useLight());
     }
 
     /**