Disallow re-sizing within crOS account addition dialog

Adding SAML federated GSuite accounts in Chrome OS Account Manager
requires loading non-GAIA URLs inside the Account Manager account
additon dialog. Loading these pages triggers a 'resize' event from
|authenticator.js|, which in turn causes the opening of a Chrome browser
window behind the account addition dialog.

|authenticator.js| accepts a parameter: |dontResizeNonEmbeddedPages| to
disable this behaviour. Use that on Chrome OS.

Bug: 962484
Test: Manually
Change-Id: I3014c8bc827f63a52847ebd7ce2e6a76950f7791
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1609832Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659092}

chrome/browser/ui/webui/signin/inline_login_handler_chromeos.cc

@@ -124,6 +124,7 @@ void InlineLoginHandlerChromeOS::SetExtraInitParams(
 
   params.SetKey("constrained", base::Value("1"));
   params.SetKey("flow", base::Value("crosAddAccount"));
+  params.SetBoolean("dontResizeNonEmbeddedPages", true);
 }
 
 void InlineLoginHandlerChromeOS::CompleteLogin(const std::string& email,