Navigation buttons should not enable if user can not navigate

content/shell/android/java/src/org/chromium/content_shell/Shell.java

Index: content/shell/android/java/src/org/chromium/content_shell/Shell.java
diff --git a/content/shell/android/java/src/org/chromium/content_shell/Shell.java b/content/shell/android/java/src/org/chromium/content_shell/Shell.java
index 9e01a9df7abfab800e63c719bd8899d005c53dec..42bcf099f86ae764255b944dc00d646088cf463d 100644
--- a/content/shell/android/java/src/org/chromium/content_shell/Shell.java
+++ b/content/shell/android/java/src/org/chromium/content_shell/Shell.java
@@ -161,6 +161,8 @@ public class Shell extends LinearLayout {
                 mPrevButton.setVisibility(hasFocus ? GONE : VISIBLE);
                 if (!hasFocus) {
                     mUrlTextView.setText(mContentViewCore.getUrl());
+                    mPrevButton.setEnabled(mContentViewCore.canGoBack());
+                    mNextButton.setEnabled(mContentViewCore.canGoForward());
                 }
             }
         });
@@ -226,7 +228,11 @@ public class Shell extends LinearLayout {
     private void onLoadProgressChanged(double progress) {
         removeCallbacks(mClearProgressRunnable);
         mProgressDrawable.setLevel((int) (10000.0 * progress));
-        if (progress == 1.0) postDelayed(mClearProgressRunnable, COMPLETED_PROGRESS_TIMEOUT_MS);
+        if (progress == 1.0) {
+            postDelayed(mClearProgressRunnable, COMPLETED_PROGRESS_TIMEOUT_MS);
+            mPrevButton.setEnabled(mContentViewCore.canGoBack());

[Ted C, 2014/05/20 22:29:37]

In my previous comment, I meant that we should actually be hooking directly into
PlatformEnableUIControl in shell_android.cc.  Currently that method is empty,
but we should just add a new method in java:

@CalledByNative
private void enableUiControl(int controlId, boolean enabled) {
    if (controlId == 0) mPrevButton.setEnabled(enabled);
    else if (controlId == 1) mNextButton.setEnabled(enabled);
}

Then we just call that from shell_android and that keeps the android port closer
to the other platforms.

+            mNextButton.setEnabled(mContentViewCore.canGoForward());
+        }
     }
 
     @CalledByNative