[Android WebView] Fix a couple of typos

Fix a couple of typos in variable names/commentary introduced in:
https://codereview.chromium.org/1315633003/

No functional effect.

BUG=156062

Review URL: https://codereview.chromium.org/1331943002

Cr-Commit-Position: refs/heads/master@{#348175}
AwMainDelegate::~AwMainDelegate() {
}

AwMainDelegate::~AwMainDelegate() {
}
