Fix synthetic wheel generation on Android

This CL adds back the source bit on injected ACTION_SCROLL motion
events.

This got lost when [1] tried to make this bit a parameter and then
subsequently removed the option due to performance regressions in [2].

The reason this breaks is because in ContentUiEventHandler.java,
onGenericMotionEvent only dispatches a wheel event if the ACTION_SCROLL
event comes from a Pointer source[3].

[1] https://crrev.com/02cd150c24de8bdebb14d88c1a144b921a47756f
[2] https://crrev.com/14e88d0ddbdd58d346bc9c3bb0629af3fdf56f0f
[3] https://cs.chromium.org/chromium/src/content/public/android/java/src/org/chromium/content/browser/ContentUiEventHandler.java?rcl=3df6abb639be7564b7743ade8db455a3564e7d32&l=67

Change-Id: I1ba4143f61ad889173735b0a168d7790a00d0865
Bug: 1025789
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1935432Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Auto-Submit: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719233}

content/browser/renderer_host/input/synthetic_input_browsertest.cc

@@ -7,13 +7,22 @@
 #include "base/run_loop.h"
 #include "base/test/test_timeouts.h"
 #include "cc/base/switches.h"
+#include "content/browser/renderer_host/input/synthetic_gesture.h"
+#include "content/browser/renderer_host/input/synthetic_smooth_scroll_gesture.h"
+#include "content/browser/renderer_host/render_widget_host_impl.h"
+#include "content/browser/web_contents/web_contents_impl.h"
 #include "content/common/input/input_event.h"
+#include "content/common/input/synthetic_gesture_params.h"
+#include "content/common/input/synthetic_smooth_scroll_gesture_params.h"
+#include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/test/browser_test_utils.h"
 #include "content/public/test/content_browser_test.h"
 #include "content/public/test/content_browser_test_utils.h"
+#include "content/public/test/hit_test_region_observer.h"
+#include "content/public/test/test_utils.h"
 #include "content/shell/browser/shell.h"
 #include "third_party/blink/public/platform/web_input_event.h"
 
@@ -27,14 +36,35 @@ class SyntheticInputTest : public ContentBrowserTest {
     command_line->AppendSwitch(cc::switches::kEnableGpuBenchmarking);
   }
 
-  RenderWidgetHost* GetRenderWidgetHost() const {
-    RenderWidgetHost* const rwh = shell()
-                                      ->web_contents()
-                                      ->GetRenderWidgetHostView()
-                                      ->GetRenderWidgetHost();
-    CHECK(rwh);
-    return rwh;
+  RenderWidgetHostImpl* GetRenderWidgetHost() const {
+    return RenderWidgetHostImpl::From(
+        shell()->web_contents()->GetRenderViewHost()->GetWidget());
   }
+
+  void LoadURL(const char* url) {
+    const GURL data_url(url);
+    EXPECT_TRUE(NavigateToURL(shell(), data_url));
+
+    RenderWidgetHostImpl* host = GetRenderWidgetHost();
+    HitTestRegionObserver observer(GetRenderWidgetHost()->GetFrameSinkId());
+    host->GetView()->SetSize(gfx::Size(400, 400));
+
+    base::string16 ready_title(base::ASCIIToUTF16("ready"));
+    TitleWatcher watcher(shell()->web_contents(), ready_title);
+    ignore_result(watcher.WaitAndGetTitle());
+
+    // Wait for the hit test data to be ready after initiating URL loading
+    // before returning
+    observer.WaitForHitTestData();
+  }
+
+  void OnSyntheticGestureCompleted(SyntheticGesture::Result result) {
+    EXPECT_EQ(SyntheticGesture::GESTURE_FINISHED, result);
+    runner_->Quit();
+  }
+
+ protected:
+  std::unique_ptr<base::RunLoop> runner_;
 };
 
 class GestureScrollObserver : public RenderWidgetHost::InputEventObserver {
@@ -76,4 +106,55 @@ IN_PROC_BROWSER_TEST_F(SyntheticInputTest, DestroyWidgetWithOngoingGesture) {
   shell()->Close();
 }
 
+// This test ensures that synthetic wheel scrolling works on all platforms.
+IN_PROC_BROWSER_TEST_F(SyntheticInputTest, SmoothScrollWheel) {
+  LoadURL(R"HTML(
+    data:text/html;charset=utf-8,
+    <!DOCTYPE html>
+    <meta name='viewport' content='width=device-width'>
+    <style>
+      body {
+        width: 10px;
+        height: 2000px;
+      }
+    </style>
+    <script>
+      document.title = 'ready';
+    </script>
+  )HTML");
+
+  SyntheticSmoothScrollGestureParams params;
+  params.gesture_source_type = SyntheticGestureParams::MOUSE_INPUT;
+  params.anchor = gfx::PointF(1, 1);
+
+  // Note: 256 is precisely chosen since Android's minimum granularity is 64px.
+  // All other platforms can specify the delta per-pixel.
+  params.distances.push_back(gfx::Vector2d(0, -256));
+
+  // Use a speed that's fast enough that the entire scroll occurs in a single
+  // GSU, avoiding precision loss. SyntheticGestures can lose delta over time
+  // in slower scrolls.
+  params.speed_in_pixels_s = 10000000.f;
+
+  // Use PrecisePixel to avoid animating.
+  params.granularity =
+      ui::input_types::ScrollGranularity::kScrollByPrecisePixel;
+
+  runner_.reset(new base::RunLoop());
+
+  std::unique_ptr<SyntheticSmoothScrollGesture> gesture(
+      new SyntheticSmoothScrollGesture(params));
+  GetRenderWidgetHost()->QueueSyntheticGesture(
+      std::move(gesture),
+      base::BindOnce(&SyntheticInputTest::OnSyntheticGestureCompleted,
+                     base::Unretained(this)));
+
+  // Run until we get the OnSyntheticGestureCompleted callback
+  runner_->Run();
+  runner_.reset();
+
+  EXPECT_EQ(256, EvalJs(shell()->web_contents(),
+                        "document.scrollingElement.scrollTop"));
+}
+
 }  // namespace content

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

@@ -156,7 +156,7 @@ public class MotionEventSynthesizerImpl implements MotionEventSynthesizer {
                 assert pointerCount == 1;
                 MotionEvent event = MotionEvent.obtain(mDownTimeInMs, timeInMs,
                         MotionEvent.ACTION_SCROLL, pointerCount, mPointerProperties, mPointerCoords,
-                        0, 0, 1, 1, 0, 0, 0, 0);
+                        0, 0, 1, 1, 0, 0, InputDevice.SOURCE_CLASS_POINTER, 0);
                 mTarget.dispatchGenericMotionEvent(event);
                 event.recycle();
                 break;