Switched to unspecified action for ACTION_IME_ENTER on Android

This CL modifies the implementation of the ACTION_IME_ENTER action
on Android to now use the EditorInfo.IME_ACTION_UNSPECIFIED value
as the editor action to perform. Previously this was set to
IME_ACTION_NEXT and in some cases was preventing the form from being
submitted.

Bug: 1057254
Change-Id: I7c429224bc7a1597ca347f079eaef463aacaea84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2145959Reviewed-by: Mark Schillaci <mschillaci@google.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Anton Vayvod <avayvod@chromium.org>
Commit-Queue: Mark Schillaci <mschillaci@google.com>
Cr-Commit-Position: refs/heads/master@{#758977}

content/public/android/java/src/org/chromium/content/browser/accessibility/WebContentsAccessibilityImpl.java

@@ -539,8 +539,9 @@ public class WebContentsAccessibilityImpl extends AccessibilityNodeProvider
         if (action == ACTION_IME_ENTER && ACTION_IME_ENTER != 0) {
             if (mWebContents != null) {
                 if (ImeAdapterImpl.fromWebContents(mWebContents) != null) {
+                    // We send an unspecified action to ensure Enter key is hit
                     return ImeAdapterImpl.fromWebContents(mWebContents)
-                            .performEditorAction(EditorInfo.IME_ACTION_NEXT);
+                            .performEditorAction(EditorInfo.IME_ACTION_UNSPECIFIED);
                 }
             }
             return false;