Explicitly flush PhishyInteractionTracker logs before destruction

Flushing at destruction time is too late since PhishyInteractionTracker
is owned by a WebContentsUserData and calls WebContentsImpl virtual
methods—specifically, WebContentsImpl::GetBrowserContext()—but
WebContentsUserData destruction does not happen until WebContentsImpl's
base classes are destroyed.

Normally, the fix would be to explicitly clear the user data early in
the destructor (e.g. see https://crrev.com/1313824); however, that turns
out to be quite difficult here because:

- WebContentsUserData cannot be destroyed before WebContentsDestroyed()
  is fired, and WebContentsDestroyed() is not fired until near the end
  of ~WebContentsImpl().

- WebContentsUserData cannot be destroyed before FrameTree, since there
  are DocumentUserData implementations that make the (reasonable)
  assumption that they will not outlive WebContentsUserData. This cannot
  be implemented without refactoring WebContents to use composition
  instead of inheritance for base::SupportsUserData.

- Even with these adjustments, MSan *still* reports a use-after-dtor
  error, since WebContentsImpl::GetBrowserContext() delegates to
  the FrameTree's NavigationController to get the BrowserContext... but
  FrameTree (and NavigationController) are destroyed before
  WebContentsUserData. 💀

Instead, since ChromePasswordReuseDetectionManagerClient is already a
WebContentsObserver and it also owns PhishyInteractiontracker, use
WebContentsDestroyed() as a signal to flush the logs and add a DCHECK()
to ~PhishyInteractionTracker() to ensure the logs were actually flushed.

Bug: 40222690
Change-Id: I298df26d0bec7e1237d70f1568d3c7ed67f0929a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5659460
Reviewed-by: Daniel Rubery <drubery@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1321152}

• chrome/browser/safe_browsing/chrome_password_reuse_detection_manager_client.cc[diff]
• chrome/browser/safe_browsing/chrome_password_reuse_detection_manager_client.h[diff]
• chrome/browser/safe_browsing/phishy_interaction_tracker.cc[diff]
• chrome/browser/safe_browsing/phishy_interaction_tracker.h[diff]