Add calls to the server to request WebAPK updates.

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java
index 86aa4f5ad46bfb55e4e1b59918aa0a6f5b735d88..968b83638ebd0a229f1b9146ddfe7fe6b0c2a54d 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebApkInstaller.java
@@ -12,7 +12,7 @@ import org.chromium.chrome.browser.ChromeApplication;
 
 /**
  * Java counterpart to webapk_installer.h
- * Contains functionality to install WebAPKs.
+ * Contains functionality to install / update WebAPKs.
  */
 public abstract class WebApkInstaller {
     /**
@@ -34,4 +34,24 @@ public abstract class WebApkInstaller {
         apkInstaller.installAsync(filePath, packageName);
         return true;
     }
+
+    /**
+     * Updates a WebAPK.
+     * @param filePath File to update.
+     * @param packageName Package name to update WebAPK at.
+     * @return True if the update was started. A "true" return value does not guarantee that the
+     *         update succeeds.
+     */
+    public abstract boolean updateAsync(String filePath, String packageName);
+
+    @CalledByNative
+    static boolean updateAsyncFromNative(String filePath, String packageName) {
+        Context context = ContextUtils.getApplicationContext();
+        WebApkInstaller apkInstaller = ((ChromeApplication) context).createWebApkInstaller();

[pkotwicz, 2016/08/08 18:59:15]

Super nit: Can this logic be moved to a function used by both
installAsyncFromNative() and updateAsyncFromNative(). Perhaps:
private static WebApkInstaller createWebApkInstaller() {}

[Xi Han, 2016/08/08 21:25:05]

Done.

+        if (apkInstaller == null) {
+            return false;
+        }
+        apkInstaller.updateAsync(filePath, packageName);
+        return true;
+    }
 }