Added a debug info UI for Blimp

blimp/client/app/android/java/src/org/chromium/blimp/session/BlimpClientSession.java

Index: blimp/client/app/android/java/src/org/chromium/blimp/session/BlimpClientSession.java
diff --git a/blimp/client/app/android/java/src/org/chromium/blimp/session/BlimpClientSession.java b/blimp/client/app/android/java/src/org/chromium/blimp/session/BlimpClientSession.java
index d16cbc2703d2178dfc79b1e6ca870fb61721f499..e5c17656459fe9e2210c0d4e84f847bd1958497b 100644
--- a/blimp/client/app/android/java/src/org/chromium/blimp/session/BlimpClientSession.java
+++ b/blimp/client/app/android/java/src/org/chromium/blimp/session/BlimpClientSession.java
@@ -47,12 +47,29 @@ public class BlimpClientSession {
          *               and their explanations.
          */
         void onDisconnected(String reason);
+
+        /**
+         * Called to update the debug UI about network statistics for the current web page.
+         * @param received Number of bytes received.
+         * @param sent Number of bytes sent.
+         * @param commit Number of commits completed.
+         */
+        void updateDebugInfo(int received, int sent, int commits);
     }
 
     private final String mAssignerUrl;
     private final List<ConnectionObserver> mObservers;
     private long mNativeBlimpClientSessionAndroidPtr;
 
+    // Flag indicating whether debug metrics are currently being displayed.
+    private boolean mStatisticsEnabled = false;
+    private int mSentOffset;
+    private int mReceivedOffset;

[Kevin M, 2016/05/20 01:02:02]

Offset => Base?

[shaktisahu, 2016/05/22 22:36:55]

Done.

+    private int mCommitsOffset;
+    private int mSent;
+    private int mReceived;
+    private int mCommits;
+
     public BlimpClientSession(String assignerUrl) {
         mAssignerUrl = assignerUrl;
         mObservers = new ArrayList<ConnectionObserver>();
@@ -162,7 +179,58 @@ public class BlimpClientSession {
         return mNativeBlimpClientSessionAndroidPtr;
     }
 
+    /**
+     * Makes a JNI call to pull the debug metrics which are asynchronously returned on callback
+     * function updateDebugStats.
+     */
+    public void getDebugStats() {
+        if (mNativeBlimpClientSessionAndroidPtr == 0) return;
+        nativeGetDebugInfo(mNativeBlimpClientSessionAndroidPtr);
+    }
+
+    /**
+     * Updates the debug metrics on the UI. Since metrics can be turned on/off any time from the UI,
+     * a snapshot of the metrics is kept the first time it is enabled and on subsequent calls this
+     * offset is subtracted from the new values to show only the difference.
+     * @param received Bytes received.
+     * @param sent Bytes sent.
+     * @param commits Commits completed.
+     */
+    @CalledByNative
+    private void updateDebugStats(int received, int sent, int commits) {
+        mReceived = received;
+        mSent = sent;
+        mCommits = commits;
+        if (!mStatisticsEnabled) {
+            mReceivedOffset = received;

[Kevin M, 2016/05/20 01:02:02]

We should probably push the offset and resetting functionality into the observer
(closer to the view), so that the data source isn't throwing away data.
Conflating state change with reset logic seems to be mixing unrelated pieces of
functionality together.

[shaktisahu, 2016/05/22 22:36:55]

Yes, I am moving it to BlimpRendererActivity to be cleaner. 

+            mSentOffset = sent;
+            mCommitsOffset = commits;
+            mStatisticsEnabled = true;
+        }
+        for (ConnectionObserver observer : mObservers) {
+            observer.updateDebugInfo(
+                    mReceived - mReceivedOffset, mSent - mSentOffset, mCommits - mCommitsOffset);
+        }
+    }
+
+    /**
+     * Resets the metrics. Currently used for displaying per navigation metrics.
+     */
+    public void resetDebugStats() {
+        mReceivedOffset = mReceived;
+        mSentOffset = mSent;
+        mCommitsOffset = mCommits;
+    }
+
+    /**
+     * Indicates that debug UI showing stats is not visible anymore.
+     */
+    public void disableDebugStats() {
+        mStatisticsEnabled = false;

[Kevin M, 2016/05/20 01:02:02]

What's the use case for statisticsEnabled? If we are only getting 1 update per
request maximum, then do we need to squelch extra updates?

[shaktisahu, 2016/05/22 22:36:55]

Actually this is a flag to the base value of the metrics. See updated comments
and naming.

+    }
+
     private native long nativeInit(String assignerUrl);
     private native void nativeConnect(long nativeBlimpClientSessionAndroid, String token);
     private native void nativeDestroy(long nativeBlimpClientSessionAndroid);
+    private native void nativeGetDebugInfo(long nativeBlimpClientSessionAndroid);
 }