Add Digital Asset Links verification for postMessage API

chrome/android/java/src/org/chromium/chrome/browser/customtabs/ClientManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/ClientManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/ClientManager.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/ClientManager.java
index 86c7219a3508ac89ba69fac1d4d3714875467eaf..5f8860d669c18c6d731b9b3f4426ea502401755c 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/ClientManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/ClientManager.java
@@ -341,6 +341,26 @@ class ClientManager {
     }
 
     /**
+     * See {@link PostMessageHandler#verifyAndInitializeWithOrigin(String, Uri)}.
+     */
+    public synchronized void verifyAndInitializeWithPostMessageOriginForSession(

[nyquist, 2017/04/19 06:35:55]

OK, I see this is used other places in this class as well, but this scares me a
little bit. By putting this on the public API of the class, you loose control of
when the lock is held and from which thread, etc. Other classes with a reference
to an instance of this object can now do:
synchronized(mClientManager) { ... }
and take the same lock as this one.

Very often, you rather want to have something like:

###
private final Object mLock = new Object();

public void something() {
  synchronized(mLock) {
    // do stuff
  }
}
###

Anyway, that sounds like something to either address or not in a follow-up, just
figured I'd mention it since I was looking :-)

[Yusuf, 2017/04/26 00:51:35]

This is more of a lizeb@ comment, because I know he likes the current structure.
But acked, I will mention this to him.

+            CustomTabsSessionToken session, Uri origin) {
+        SessionParams params = mSessionParams.get(session);
+        if (params == null) return;
+        params.postMessageHandler.verifyAndInitializeWithOrigin(params.packageName, origin);

[nyquist, 2017/04/19 06:35:55]

the |postMessageHandler| member of SessionParams seems to for example come from
#newSession(...), which is a public method, but we seem to never check whether
the PostMessageHandler reference is null.
Is that because this class is package protected, and we're guaranteed that the
caller will never pass in null?

[Yusuf, 2017/04/26 00:51:35]

Yes, the assumption is that is never null.
Would rather resolve this by adding @NonNull to newSession. (which is the case
for the current only caller.)

+    }
+
+    /**
+     * @return The postMessage origin for the given session.
+     */
+    @VisibleForTesting
+    synchronized Uri getPostMessageOriginForSessionForTesting(CustomTabsSessionToken session) {
+        SessionParams params = mSessionParams.get(session);
+        if (params == null) return null;
+        return params.postMessageHandler.getOriginForTesting();
+    }
+
+    /**
      * See {@link PostMessageHandler#reset(WebContents)}.
      */
     public synchronized void resetPostMessageHandlerForSession(