Unify stop and close X buttons.

BUG=455002

Review URL: https://codereview.chromium.org/897933002

Cr-Commit-Position: refs/heads/master@{#314619}

chrome/android/shell/java/src/org/chromium/chrome/shell/ChromeShellToolbar.java

@@ -50,7 +50,7 @@ public class ChromeShellToolbar extends LinearLayout {
             mProgressDrawable.setLevel(100 * mProgress);
             if (mLoading) {
                 mStopReloadButton.setImageResource(
-                        R.drawable.btn_toolbar_stop);
+                        R.drawable.btn_close);
             } else {
                 mStopReloadButton.setImageResource(R.drawable.btn_toolbar_reload);
                 ApiCompatibilityUtils.postOnAnimationDelayed(ChromeShellToolbar.this,

chrome/android/shell/res/layout/chrome_shell_activity.xml

@@ -27,7 +27,7 @@
             android:id="@+id/stop_reload_button"
             android:layout_width="38dp"
             android:layout_height="38dp"
-            android:src="@drawable/btn_toolbar_stop"
+            android:src="@drawable/btn_close"
             android:background="?attr/selectableItemBackground"
             android:scaleType="center"/>
         <EditText android:id="@+id/url"