aw: Keep selection handles when flinging

Currently, PopupWindow-based selection handles are hidden when scrolling
begins. However, WebView uses an entirely separate code path for flings,
about which PopupWindow knows nothing. Thus, the handles could
re-appear in the middle of a View-driven fling.

Expose whether such a fling is active via the ContentViewClient, making
such information available to the selection handle visibility logic.
This ensures the handles stay hidden for the duration of the fling.

Review URL: https://codereview.chromium.org/958673003

Cr-Commit-Position: refs/heads/master@{#318080}

android_webview/java/src/org/chromium/android_webview/AwContentViewClient.java

@@ -133,4 +133,9 @@ public class AwContentViewClient extends ContentViewClient implements ContentVid
     public boolean isJavascriptEnabled() {
         return mAwSettings != null && mAwSettings.getJavaScriptEnabled();
     }
+
+    @Override
+    public boolean isExternalFlingActive() {
+        return mAwContents.isFlingActive();
+    }
 }

android_webview/java/src/org/chromium/android_webview/AwContents.java

@@ -2250,7 +2250,7 @@ public class AwContents implements SmartClipProvider,
     }
 
     @CalledByNative
-    private boolean isFlingActive() {
+    public boolean isFlingActive() {
         return mScrollOffsetManager.isFlingActive();
     }
 

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

@@ -162,6 +162,14 @@ public class ContentViewClient {
         return true;
     }
 
+    /**
+     * @return Whether an externally managed (i.e., not compositor-driven) fling
+     *         of this ContentView is active.
+     */
+    public boolean isExternalFlingActive() {
+        return false;
+    }
+
     /**
      * Check whether a key should be propagated to the embedder or not.
      * We need to send almost every key to Blink. However:

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

@@ -1180,7 +1180,9 @@ public class ContentViewCore
     }
 
     public boolean isScrollInProgress() {
-        return mTouchScrollInProgress || mPotentiallyActiveFlingCount > 0;
+        return mTouchScrollInProgress
+                || mPotentiallyActiveFlingCount > 0
+                || getContentViewClient().isExternalFlingActive();
     }
 
     @SuppressWarnings("unused")