Mirror the crbug.com/40679846 mitigation on the CustomButtonParams bottom-bar
path: stop assigning the embedder-supplied int as a live View ID inside
Chrome's Activity hierarchy. Store it as a View tag instead and look it up
via findViewWithTag() in the one place that needs it.

--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomButtonParamsImpl.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomButtonParamsImpl.java
@@ -161,8 +161,11 @@ public class CustomButtonParamsImpl implements CustomButtonParams {
         ImageButton button =
                 (ImageButton)
                         LayoutInflater.from(context)
                                 .inflate(R.layout.custom_tabs_bottombar_item, parent, false);
-        button.setId(mId);
+        // Do NOT setId(mId): mId is embedder-supplied and would shadow Chrome's
+        // own R.id.* in Activity.findViewById(). See http://crbug.com/40679846
+        // (the RemoteViews path strips IDs for the same reason).
+        button.setTag(mId);
         button.setImageDrawable(getIcon(context, buttonIconTint));
         button.setContentDescription(mDescription);
         if (mPendingIntent == null) {
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabBottomBarDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabBottomBarDelegate.java
@@ -238,7 +238,8 @@ public class CustomTabBottomBarDelegate
         if (mCustomButtonsUpdater != null && mCustomButtonsUpdater.updateBottomBarButton(params)) {
             return;
         }
-        ImageButton button = getBottomBarView().findViewById(params.getId());
+        // Embedder IDs are stored as tags, not view IDs (crbug.com/40679846).
+        ImageButton button = (ImageButton) getBottomBarView().findViewWithTag(params.getId());
         button.setContentDescription(params.getDescription());
         button.setImageDrawable(params.getIcon(mActivity, getButtonIconTint()));
     }