WebView: use proper javadocs

Javadocs need to start with "/**", not "/*". This can unexpectedly
trigger a presubmit failure if someone changes something else in these
methods.

This also fixes an import-order presubmit error.

Bug: 65553544
Test: make -j30 docs (no visible change)
Change-Id: I1bc8ef479e3dc9378e58904d0b317c4775117390