Refactor Clipboard Last Modified Time Storage

ui/android/java/src/org/chromium/ui/base/Clipboard.java

Index: ui/android/java/src/org/chromium/ui/base/Clipboard.java
diff --git a/ui/android/java/src/org/chromium/ui/base/Clipboard.java b/ui/android/java/src/org/chromium/ui/base/Clipboard.java
index abfdf2e01f6d2492f36baedef83074d7432509f0..5f145fca0aab6898fc5064b39c93d1c53bfca3fa 100644
--- a/ui/android/java/src/org/chromium/ui/base/Clipboard.java
+++ b/ui/android/java/src/org/chromium/ui/base/Clipboard.java
@@ -9,19 +9,13 @@ import android.content.ClipboardManager;
 import android.content.Context;
 
 import org.chromium.base.ContextUtils;
-import org.chromium.base.Log;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.annotations.SuppressFBWarnings;
-import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.base.metrics.RecordUserAction;
 import org.chromium.ui.R;
 import org.chromium.ui.widget.Toast;
 
-import java.security.MessageDigest;
-import java.security.NoSuchAlgorithmException;
-import java.util.Arrays;
-
 /**
  * Simple proxy that provides C++ code with an access pathway to the Android clipboard.
  */
@@ -29,25 +23,12 @@ import java.util.Arrays;
 public class Clipboard implements ClipboardManager.OnPrimaryClipChangedListener {
     private static Clipboard sInstance;
 
-    private static final String TAG = "Clipboard";
-
     // Necessary for coercing clipboard contents to text if they require
     // access to network resources, etceteras (e.g., URI in clipboard)
     private final Context mContext;
 
     private final ClipboardManager mClipboardManager;
 
-    // A message hasher that's used to hash clipboard contents so we can tell
-    // when a clipboard changes without storing the full contents.
-    private MessageDigest mMd5Hasher;
-    // The hash of the current clipboard.
-    // TODO(mpearson): unsuppress this warning once saving and restoring
-    // the hash from prefs is added.
-    @SuppressFBWarnings("URF_UNREAD_FIELD")
-    private byte[] mClipboardMd5;
-    // The time when the clipboard was last updated.  Set to 0 if unknown.
-    private long mClipboardChangeTime;
-
     /**
      * Get the singleton Clipboard instance (creating it if needed).
      */
@@ -65,19 +46,6 @@ public class Clipboard implements ClipboardManager.OnPrimaryClipChangedListener
                 (ClipboardManager) ContextUtils.getApplicationContext().getSystemService(
                         Context.CLIPBOARD_SERVICE);
         mClipboardManager.addPrimaryClipChangedListener(this);
-        try {
-            mMd5Hasher = MessageDigest.getInstance("MD5");
-            mClipboardMd5 = weakMd5Hash();
-        } catch (NoSuchAlgorithmException e) {
-            Log.e(TAG,
-                    "Unable to construct MD5 MessageDigest: %s; assume "
-                            + "clipboard last update time is start of epoch.",
-                    e);
-            mMd5Hasher = null;
-            mClipboardMd5 = new byte[] {};
-        }
-        RecordHistogram.recordBooleanHistogram("Clipboard.ConstructedHasher", mMd5Hasher != null);
-        mClipboardChangeTime = 0;
     }
 
     /**
@@ -129,21 +97,6 @@ public class Clipboard implements ClipboardManager.OnPrimaryClipChangedListener
     }
 
     /**
-     * Gets the time the clipboard content last changed.
-     *
-     * This is calculated according to the device's clock.  E.g., it continues
-     * increasing when the device is suspended.  Likewise, it can be in the
-     * future if the user's clock updated after this information was recorded.
-     *
-     * @return a Java long recording the last changed time in milliseconds since
-     * epoch, or 0 if the time could not be determined.
-     */
-    @CalledByNative
-    public long getClipboardContentChangeTimeInMillis() {
-        return mClipboardChangeTime;
-    }
-
-    /**
      * Emulates the behavior of the now-deprecated
      * {@link android.text.ClipboardManager#setText(CharSequence)}, setting the
      * clipboard's current primary clip to a plain-text clip that consists of
@@ -190,35 +143,17 @@ public class Clipboard implements ClipboardManager.OnPrimaryClipChangedListener
     }
 
     /**
-     * Updates mClipboardMd5 and mClipboardChangeTime when the clipboard updates.
+     * Tells the C++ Clipboard that the clipboard has changed.
      *
      * Implements OnPrimaryClipChangedListener to listen for clipboard updates.
      */
     @Override
     public void onPrimaryClipChanged() {
-        if (mMd5Hasher == null) return;
         RecordUserAction.record("MobileClipboardChanged");
-        mClipboardMd5 = weakMd5Hash();
-        // Always update the clipboard change time even if the clipboard
-        // content hasn't changed.  This is because if the user put something
-        // in the clipboard recently (even if it was not necessary because it
-        // was already there), that content should be considered recent.
-        mClipboardChangeTime = System.currentTimeMillis();
+        long nativeClipboardAndroid = nativeInit();
+        if (nativeClipboardAndroid != 0) nativeOnPrimaryClipChanged(nativeClipboardAndroid);
     }
 
-    /**
-     * Returns a weak hash of getCoercedText().
-     *
-     * @return a Java byte[] with the weak hash.
-     */
-    private byte[] weakMd5Hash() {
-        if (getCoercedText() == null) {
-            return new byte[] {};
-        }
-        // Compute a hash consisting of the first 4 bytes of the MD5 hash of
-        // getCoercedText().  This value is used to detect clipboard content
-        // change. Keeping only 4 bytes is a privacy requirement to introduce
-        // collision and allow deniability of having copied a given string.
-        return Arrays.copyOfRange(mMd5Hasher.digest(getCoercedText().getBytes()), 0, 4);
-    }
+    private native long nativeInit();
+    private native void nativeOnPrimaryClipChanged(long nativeClipboardAndroid);
 }