Revert "Android: Private-package Tab.setIsShowingErroPage"

This reverts commit 1e252fbf.

Reason for revert: this change broke the internal build https://ci.chromium.org/p/chrome/builders/ci/android-internal-chromium-tot/b8898843520461106640

Also, TabTestUtils.setIsShowingErrorPage() isn't defined as static, so the error couldn't be fixed in 1 internal CL. 

Original change's description:
> Android: Private-package Tab.setIsShowingErroPage
> 
> The method is called by a class in chrome.browser.tab package
> in production code. Makes it a private-package method.
> 
> Bug: 995903
> Change-Id: I5f8b73200ae4a3c966b140a44e63cfc991f9b249
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872079
> Reviewed-by: David Trainor <dtrainor@chromium.org>
> Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#708466}

TBR=dtrainor@chromium.org,jinsukkim@chromium.org

Change-Id: Ieed0cf2e34f59cf4f7e68a4eb44dea0ea2f561aa
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 995903
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1876389Reviewed-by: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708594}

chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java

@@ -467,7 +467,7 @@ public class Tab {
      *
      * @param isShowingErrorPage Whether the tab shows an error page.
      */
-    void setIsShowingErrorPage(boolean isShowingErrorPage) {
+    public void setIsShowingErrorPage(boolean isShowingErrorPage) {
         mIsShowingErrorPage = isShowingErrorPage;
     }
 

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

@@ -111,14 +111,4 @@ public class TabTestUtils {
             Tab tab, WebContents webContents, boolean didStartLoad, boolean didFinishLoad) {
         tab.swapWebContents(webContents, didStartLoad, didFinishLoad);
     }
-
-    /**
-     * 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 void setIsShowingErrorPage(Tab tab, boolean isShowingErrorPage) {
-        tab.setIsShowingErrorPage(isShowingErrorPage);
-    }
 }