[Blink] Don't select placeholder text in <input> when long press below.

https://crbug.com/873999 shows that placeholder text in <input> could
be selected by long press below it.

This is because for this code path we passed a corrected click point.
y-coordinate was adjusted to 0, which will lead
|LayoutBlock::PositionForPointIfOutsideAtomicInlineLevel()| give a
incorrect result, then in
|SelectionController::SelectClosestWordFromHitTestResult()|, it gets
the placeholder <div> in the <input> Shadow DOM as the hit test result
position.

We now pass the normal point so it could figure out the position is
at <input>, which is more reasonable.

Bug: 873999
Change-Id: I6d9ee4d03778ad65493eff8735d58cf271d07a57
Reviewed-on: https://chromium-review.googlesource.com/1174963
Commit-Queue: Shimi Zhang <ctzsm@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585208}

third_party/blink/renderer/core/exported/web_view_test.cc

@@ -1024,6 +1024,32 @@ TEST_F(WebViewTest, FinishComposingTextDoesNotAssert) {
       WebInputMethodController::kKeepSelection);
 }
 
+// Regression test for https://crbug.com/873999
+TEST_F(WebViewTest, LongPressOutsideInputShouldNotSelectPlaceholderText) {
+  RegisterMockedHttpURLLoad("input_placeholder.html");
+  WebViewImpl* web_view =
+      web_view_helper_.InitializeAndLoad(base_url_ + "input_placeholder.html");
+  web_view->SetInitialFocus(false);
+  web_view->Resize(WebSize(500, 300));
+  web_view->UpdateAllLifecyclePhases();
+  RunPendingTasks();
+
+  WebString input_id = WebString::FromUTF8("input");
+
+  // Focus in input.
+  EXPECT_TRUE(TapElementById(WebInputEvent::kGestureTap, input_id));
+
+  // Long press below input.
+  WebGestureEvent event(WebInputEvent::kGestureLongPress,
+                        WebInputEvent::kNoModifiers,
+                        WebInputEvent::GetStaticTimeStampForTests(),
+                        kWebGestureDeviceTouchscreen);
+  event.SetPositionInWidget(WebFloatPoint(100, 150));
+  EXPECT_EQ(WebInputEventResult::kHandledSystem,
+            web_view->HandleInputEvent(WebCoalescedInputEvent(event)));
+  EXPECT_TRUE(web_view->MainFrameImpl()->SelectionAsText().IsEmpty());
+}
+
 TEST_F(WebViewTest, FinishComposingTextCursorPositionChange) {
   RegisterMockedHttpURLLoad("input_field_populated.html");
   WebViewImpl* web_view = web_view_helper_.InitializeAndLoad(

third_party/blink/renderer/core/layout/layout_block_flow.cc

@@ -4757,14 +4757,20 @@ PositionWithAffinity LayoutBlockFlow::PositionForPoint(
       }
     }
 
+    if (closest_box->GetLineLayoutItem().IsAtomicInlineLevel()) {
+      // We want to pass the original point other than a corrected one.
+      LayoutPoint point(point_in_logical_contents);
+      if (!IsHorizontalWritingMode())
+        point = point.TransposedPoint();
+      return PositionForPointRespectingEditingBoundaries(
+          LineLayoutBox(closest_box->GetLineLayoutItem()), point);
+    }
+
     // pass the box a top position that is inside it
     LayoutPoint point(point_in_logical_contents.X(),
                       closest_box->Root().BlockDirectionPointInLine());
     if (!IsHorizontalWritingMode())
       point = point.TransposedPoint();
-    if (closest_box->GetLineLayoutItem().IsAtomicInlineLevel())
-      return PositionForPointRespectingEditingBoundaries(
-          LineLayoutBox(closest_box->GetLineLayoutItem()), point);
     return closest_box->GetLineLayoutItem().PositionForPoint(point);
   }
 

third_party/blink/renderer/core/testing/data/input_placeholder.html

+<input id="input" type="text" name="name" placeholder="username" />