Convert Web Store Inline Install IPCs to mojo

chrome/common/extensions/mojo/inline_install.mojom

+// Copyright 2017 The Chromium Authors. All rights reserved.

[Ken Rockot(use gerrit already), 2017/05/08 16:12:45]

minor nit: Moving forward, we would prefer that if a subdirectory is dedicated
to mojom+typemap+traits definitions, it be named "mojom" instead of "mojo".
We'll be adapting other directories to follow that pattern as well.

[catmullings, 2017/05/08 20:41:35]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module extensions.mojom;
+
+[Native]
+enum WebstoreInstallResult;
+
+[Native]
+enum WebstoreInstallStage;
+
+interface InlineInstallProgressListener {
+  // Notifies the renderer once the installation mentioned on
+  // InlineWebstoreInstall is complete.
+  InlineInstallResponse(int32 install_id, bool success, string error,

[Ken Rockot(use gerrit already), 2017/05/08 16:12:45]

I may be overlooking something. At a glance it seems like install_id is only
used to link a response to the original request. Is that accurate? If so, this
message could just be a reply to DoInlineInstall, e.g.:


interface InlineInstaller {
  DoInlineInstall(string webstore_item_id, int32 listeners_mask,
                  InlineInstallProgressListener install_progress_listener)
      => (bool success, string error, WebStoreInstallResult result);
};

[catmullings, 2017/05/08 20:41:35]

Yes, install_id is only used to link the response to the original request.
However, there is an intentional reason why InlineInstallResponse is a separate
mojo message. In the case when an inline installation does not complete, the
callback response would never be called, causing a mojo error.

One workaround I considered was manually closing the pipe connection in that
case. However, the pipe would need to be closed on WebstoreInstaller (when the
installation incompletion occurs), which conceptually wasn't the best solution
because pipe closing should be isolated to the tab helper. 

+      WebstoreInstallResult result);
+
+  // Notifies the renderer when install stage updates were requested for an
+  // inline install.
+  InlineInstallStageChanged(WebstoreInstallStage stage);
+
+  // Notifies the renderer when download progress updates were requested for an
+  // inline install.
+  InlineInstallDownloadProgress(int32 percent_downloaded);
+};
+
+interface InlineInstaller {
+  // Sent by the renderer to implement chrome.webstore.install().
+  DoInlineInstall(
+      int32 install_id, string webstore_item_id, int32 listeners_mask,
+      InlineInstallProgressListener install_progress_listener);
+};
+
+