Start action mode even if clipboard is empty

Previously clank would not call View#startActionMode for a FloatingPastePopup menu
if the copy/paste clipboard was empty (because there would be nothing in the menu).
This is a problem because apps using WebView may want to add items to the
FloatingPastePopup menu (using startActionMode) even if the clipboard is empty.

This patch makes clank call View#startActionMode and make an empty menu when there
is nothing to paste.

BUG=652916

Review-Url: https://codereview.chromium.org/2443963003
Cr-Commit-Position: refs/heads/master@{#427210}

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

@@ -2525,7 +2525,7 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Displa
             return;
         }
 
-        if (!mHasInsertion || !canPaste()) return;
+        if (!mHasInsertion || (!supportsFloatingActionMode() && !canPaste())) return;
 
         PastePopupMenu pastePopupMenu = getPastePopup();
         if (pastePopupMenu == null) return;

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

@@ -174,6 +174,10 @@ public class WebActionModeCallback implements ActionMode.Callback {
             new MenuInflater(getContext()).inflate(R.menu.select_action_menu, menu);
         }
 
+        if (!mEditable || !canPaste()) {
+            menu.removeItem(R.id.select_action_menu_paste);
+        }
+
         if (mIsInsertion) {
             menu.removeItem(R.id.select_action_menu_select_all);
             menu.removeItem(R.id.select_action_menu_cut);
@@ -183,10 +187,6 @@ public class WebActionModeCallback implements ActionMode.Callback {
             return;
         }
 
-        if (!mEditable || !canPaste()) {
-            menu.removeItem(R.id.select_action_menu_paste);
-        }
-
         if (!mEditable) {
             menu.removeItem(R.id.select_action_menu_cut);
         }