Consolidate javascript_dialog_manager.h and javascript_dialog_manager_impl.h

* Renamed JavaScriptDialgoManagerImpl to JavaScriptDialogManager.
* Add namespace app_modal_dialogs
* Add namespace javascript_dialog_extensions_client
* Shortened InstallJavaScriptDialogExtensionsClient to InstallClient to fit the 80 chars limit.

BUG=410499
[email protected]

Review URL: https://codereview.chromium.org/688853005

Cr-Commit-Position: refs/heads/master@{#304903}
43 files changed