PlzNavigate: Use WebNavigationPolicyHandledByClient

When PlzNavigate is enabled, this CL has
RenderFrameImpl::decidePolicyForNavigation return
WebNavigationPolicyHandledByClient when the navigation is sent ot the browser.
Before it would return WebNavigationPolicyIgnore, which would result in an
incorrect tracking of load state in the renderer.

BUG=576265
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review URL: https://codereview.chromium.org/1608283002

Cr-Commit-Position: refs/heads/master@{#376761}
8 files changed