Delete unneeded pending entries in DidFailProvisionalLoad to prevent a spoof.

BUG=280512
BUG=278899
TEST=See bug for repro steps.

Review URL: https://chromiumcodereview.appspot.com/23978003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222146 0039d316-1c4b-4281-b951-d872f2087c98
  void TakeScreenshotFor(content::NavigationEntryImpl* entry) {
    SkBitmap bitmap;
    bitmap.setConfig(SkBitmap::kARGB_8888_Config, 1, 1);
    bitmap.allocPixels();
    bitmap.eraseRGB(0, 0, 0);
    encoding_screenshot_in_progress_ = true;
    OnScreenshotTaken(entry->GetUniqueID(), true, bitmap);
    WaitUntilScreenshotIsReady();
  }

  void TakeScreenshotFor(content::NavigationEntryImpl* entry) {
    SkBitmap bitmap;
    bitmap.setConfig(SkBitmap::kARGB_8888_Config, 1, 1);
    bitmap.allocPixels();
    bitmap.eraseRGB(0, 0, 0);
    encoding_screenshot_in_progress_ = true;
    OnScreenshotTaken(entry->GetUniqueID(), true, bitmap);
    WaitUntilScreenshotIsReady();
  }
