Introduce ThreadedInputConnection behind a switch

content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java

Index: content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
index e6eb23a536823ecf8c691e22078af60c14dc27e6..d1eb7eadf1c34c1831a9c4597a380185e12595a2 100644
--- a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
+++ b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
@@ -334,6 +334,7 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Screen
             contentViewCore.mIsMobileOptimizedHint = false;
             contentViewCore.hidePopupsAndClearSelection();
             contentViewCore.resetScrollInProgress();
+            contentViewCore.resetImeAdapter();
         }
 
         private void determinedProcessVisibility() {
@@ -934,6 +935,7 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Screen
         mWebContentsObserver = null;
         setSmartClipDataListener(null);
         setZoomControlsDelegate(null);
+        mImeAdapter.reset();
         // TODO(igsolla): address TODO in ContentViewClient because ContentViewClient is not
         // currently a real Null Object.
         //
@@ -3095,6 +3097,11 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Screen
         }
     }
 
+    @VisibleForTesting
+    public WebContentsObserver getWebContentsObserverForTest() {
+        return mWebContentsObserver;
+    }
+
     /**
      * Offer a long press gesture to the embedding View, primarily for WebView compatibility.
      *
@@ -3120,6 +3127,10 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Screen
         if (potentiallyActiveFlingCount > 0) updateGestureStateListener(GestureEventType.FLING_END);
     }
 
+    private void resetImeAdapter() {
+        mImeAdapter.reset();
+    }
+
     private float getWheelScrollFactorInPixels() {
         if (mWheelScrollFactorInPixels == 0) {
             TypedValue outValue = new TypedValue();