Don't clear pending NavigationParams until didStopLoading.

Clearing them at the end of NavigateInternal causes problems when a
ScopedPageLoadDeferrer is in use.

Credit to thestig@ for the test framework changes.

BUG=626838
TEST=See bug for repro steps.

Review-Url: https://codereview.chromium.org/2140393002
Cr-Commit-Position: refs/heads/master@{#407239}
2 files changed