Clean up app launcher flag descriptions for grammar and consistency.

Consistently use the phrase "App Launcher" (not "App List" or "app
launcher").

BUG=248353

Review URL: https://codereview.chromium.org/165943002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251637 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251637
Cleanup: Move WebLayerTreeViewImplForTesting into content namespace.

BUG=338153
TEST=content_unittests
TBR=jam@chromium.org

Review URL: https://codereview.chromium.org/169133002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251638 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251638