Android: TabTestUtil.setIsShowingErrorPage

Moved the method from clank/javatests/../TabUtils.java. This CL needs
landing before the clank side change happens to keep the build green.
https://crrev.com/i/2788136

TBR=tedchoc@chromium.org

Bug: 995903
Change-Id: I43df78505c99ee60d3fb11df44a25a7e6e02c776
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2111812Reviewed-by: Jinsuk Kim <jinsukkim@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751944}

chrome/test/android/javatests/src/org/chromium/chrome/browser/tab/TabTestUtils.java

@@ -134,4 +134,14 @@ public class TabTestUtils {
     public static TabWebContentsDelegateAndroid getTabWebContentsDelegate(Tab tab) {
         return ((TabImpl) tab).getTabWebContentsDelegateAndroid();
     }
+
+    /**
+     * Sets whether the tab is showing an error page.  This is reset whenever the tab finishes a
+     * navigation.
+     * @param tab {@link Tab} object.
+     * @param isShowingErrorPage Whether the tab shows an error page.
+     */
+    public static void setIsShowingErrorPage(Tab tab, boolean isShowingErrorPage) {
+        ((TabImpl) tab).setIsShowingErrorPage(isShowingErrorPage);
+    }
 }