Use in-class initializers for base::WeakPtrFactory in chrome/.

Generated by: https://chromium-review.googlesource.com/c/chromium/src/+/1689216

Some existing uses of NULL are replaced with nullptr to remove
presubmit errors.

Bug: 981415
Change-Id: I9824a00bd16e27cf2f0e03e6c7127ffc457b56e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697372
Commit-Queue: Jeremy Roman <[email protected]>
Reviewed-by: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#676912}
diff --git a/chrome/browser/extensions/external_install_error.cc b/chrome/browser/extensions/external_install_error.cc
index c10c8696..cb4172f 100644
--- a/chrome/browser/extensions/external_install_error.cc
+++ b/chrome/browser/extensions/external_install_error.cc
@@ -337,8 +337,7 @@
       alert_type_(alert_type),
       manager_(manager),
       error_service_(GlobalErrorServiceFactory::GetForProfile(
-          Profile::FromBrowserContext(browser_context_))),
-      weak_factory_(this) {
+          Profile::FromBrowserContext(browser_context_))) {
   prompt_.reset(new ExtensionInstallPrompt::Prompt(
       ExtensionInstallPrompt::EXTERNAL_INSTALL_PROMPT));