Move JavaScriptDialogManager, JavascriptAppModalDialogViews to components/app_modal_dialogs.
(I first tried to move cocoa/android impl, but it turns out to be more difficult than I originally thought so I left them as they are)

Introduced JavaScriptDialogManagerClient for embedder to implement extensions related behaviors.

BUG=410499
[email protected]

Review URL: https://codereview.chromium.org/666533007

Cr-Commit-Position: refs/heads/master@{#303004}
diff --git a/chrome/browser/DEPS b/chrome/browser/DEPS
index cf13524..96f0df4 100644
--- a/chrome/browser/DEPS
+++ b/chrome/browser/DEPS
@@ -89,6 +89,7 @@
   "+device/media_transfer_protocol",
   "+extensions/browser",
   "+extensions/common",
+  "+extensions/components/javascript_dialog_extensions_client",
   "+extensions/grit",
   "+extensions/test",
   "+google/cacheinvalidation",  # Sync invalidation API protobuf files.