Make the webstore inline install dialog be tab-modal

Also clean up a few minor lint errors while I'm in here.

BUG=550047

Review URL: https://codereview.chromium.org/1496033003

Cr-Commit-Position: refs/heads/master@{#363925}
void ExtensionInstallPrompt::OnInstallSuccess(const Extension* extension,
                                              SkBitmap* icon) {
  extension_ = extension;
  SetIcon(icon);

  install_ui_->OnInstallSuccess(extension, &icon_);
}

void ExtensionInstallPrompt::OnInstallSuccess(const Extension* extension,
                                              SkBitmap* icon) {
  extension_ = extension;
  SetIcon(icon);

  install_ui_->OnInstallSuccess(extension, &icon_);
}
