Rename infobar_close_button to btn_close.

This asset is also used in internal repository.

BUG=453995

Review URL: https://codereview.chromium.org/886193002

Cr-Commit-Position: refs/heads/master@{#314115}

chrome/android/java/res/layout/app_banner_view.xml

@@ -75,7 +75,7 @@
                 android:id="@+id/close_button"
                 android:contentDescription="@string/infobar_close"
                 android:adjustViewBounds="true"
-                android:src="@drawable/infobar_close_button"
+                android:src="@drawable/btn_close"
                 android:background="@drawable/app_banner_button_close"
                 android:padding="@dimen/app_banner_close_button_padding"
                 android:layout_width="wrap_content"

chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarLayout.java

@@ -157,7 +157,7 @@ public class InfoBarLayout extends ViewGroup implements View.OnClickListener {
         // Set up the close button. Apply padding so it has a big touch target.
         mCloseButton = new ImageButton(context);
         mCloseButton.setId(R.id.infobar_close_button);
-        mCloseButton.setImageResource(R.drawable.infobar_close_button);
+        mCloseButton.setImageResource(R.drawable.btn_close);
         TypedArray a = getContext().obtainStyledAttributes(
                 new int [] {R.attr.selectableItemBackground});
         Drawable closeButtonBackground = a.getDrawable(0);