Rename java WebContentsObserverAndroid to WebContentsObserver
The Java class org.chromium.content.browser.WebContentsObserverAndroid
is incorrectly named and should be WebContentsObserver to follow
the same pattern as for other classes.
The current WebContentsObserverAndroid is deprecated and it extends
new class WebContentsObserver inorder to delegate all method calls.
This is done for external repositories to adapt new class name to
WebContentsObserver after this change.
Once this is done WebContentsObserverAndroid will be removed in
next patch.
BUG=396118
Review URL: https://codereview.chromium.org/
589113002
Cr-Commit-Position: refs/heads/master@{#299923}