Added experimental Share API on Android behind flag.

chrome/android/java/src/org/chromium/chrome/browser/webshare/ShareServiceImpl.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webshare/ShareServiceImpl.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webshare/ShareServiceImpl.java b/chrome/android/java/src/org/chromium/chrome/browser/webshare/ShareServiceImpl.java
new file mode 100644
index 0000000000000000000000000000000000000000..4a69fea08b85a6f882501dce2acff8354efbe478
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webshare/ShareServiceImpl.java
@@ -0,0 +1,77 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.webshare;
+
+import android.content.Context;
+import android.content.Intent;
+
+import org.chromium.chrome.R;
+import org.chromium.content.browser.ContentViewCore;
+import org.chromium.content_public.browser.WebContents;
+import org.chromium.mojo.system.MojoException;
+import org.chromium.mojom.webshare.ShareService;
+import org.chromium.ui.base.WindowAndroid;
+
+/**
+ * Android implementation of the ShareService service defined in
+ * third_party/WebKit/public/platform/modules/webshare/webshare.mojom.
+ */
+public class ShareServiceImpl implements ShareService {
+    private final WindowAndroid mWindow;
+    private final Context mContext;
+
+    public ShareServiceImpl(WebContents webContents) {
+        mWindow = windowFromWebContents(webContents);
+        mContext = contextFromWindow(mWindow);
+    }
+
+    @Override
+    public void close() {}
+
+    @Override
+    public void onConnectionError(MojoException e) {}
+
+    @Override
+    public void share(String title, String text, ShareResponse callback) {
+        if (mContext == null) {
+            callback.call("Share failed");
+            return;
+        }
+
+        String chooserTitle = mContext.getString(R.string.share_link_chooser_title);
+        Intent send = new Intent(Intent.ACTION_SEND);
+        send.setType("text/plain");
+        send.putExtra(Intent.EXTRA_SUBJECT, text);

[gone, 2016/07/28 16:03:20]

Shouldn't this be title?

[Matt Giuca, 2016/07/29 01:43:03]

Done. #oops

+        send.putExtra(Intent.EXTRA_TEXT, text);
+
+        Intent chooser = Intent.createChooser(send, chooserTitle);
+        if (!mWindow.showIntent(chooser, null, null)) {
+            callback.call("Share failed");
+            return;
+        }
+
+        // Success.
+        // TODO(mgiuca): Wait until the user has made a choice, and report failure if they cancel
+        // the picker or something else goes wrong.
+        callback.call(null);
+    }
+
+    // |webContents| can be null. Can return null.

[gone, 2016/07/28 16:03:20]

Use real Javadoc-style comments.  Optionally use the @Nullable annotation on the
webContents parameter:
https://developer.android.com/reference/android/support/annotation/Nullable.html

[Matt Giuca, 2016/07/29 01:43:03]

Done.

+    private static WindowAndroid windowFromWebContents(WebContents webContents) {
+        if (webContents == null) return null;
+
+        ContentViewCore contentViewCore = ContentViewCore.fromWebContents(webContents);
+        if (contentViewCore == null) return null;
+
+        return contentViewCore.getWindowAndroid();
+    }
+
+    // |window| can be null. Can return null.
+    private static Context contextFromWindow(WindowAndroid window) {
+        if (window == null) return null;
+
+        return window.getActivity().get();
+    }
+}