Make SyntheticPointerAction to flush the pointer action sequence

content/browser/renderer_host/input/synthetic_mouse_driver.cc

Index: content/browser/renderer_host/input/synthetic_mouse_driver.cc
diff --git a/content/browser/renderer_host/input/synthetic_mouse_driver.cc b/content/browser/renderer_host/input/synthetic_mouse_driver.cc
index 82dcbdd8a413df55d939127dc47de124f90d9822..32887e0dd081ee4a8b192819e13f9c91a1147713 100644
--- a/content/browser/renderer_host/input/synthetic_mouse_driver.cc
+++ b/content/browser/renderer_host/input/synthetic_mouse_driver.cc
@@ -18,11 +18,11 @@ void SyntheticMouseDriver::DispatchEvent(SyntheticGestureTarget* target,
   target->DispatchInputEventToPlatform(mouse_event_);
 }
 
-int SyntheticMouseDriver::Press(float x, float y) {
+void SyntheticMouseDriver::Press(float x, float y, int index) {
+  DCHECK_EQ(index, 0);
   mouse_event_ = SyntheticWebMouseEventBuilder::Build(
       blink::WebInputEvent::MouseDown, x, y, 0);
   mouse_event_.clickCount = 1;
-  return 0;
 }
 
 void SyntheticMouseDriver::Move(float x, float y, int index) {
@@ -44,9 +44,7 @@ void SyntheticMouseDriver::Release(int index) {
 
 bool SyntheticMouseDriver::UserInputCheck(
     const SyntheticPointerActionParams& params) const {
-  if (params.gesture_source_type != SyntheticGestureParams::MOUSE_INPUT)
-    return false;
-
+  DCHECK_EQ(params.index(), 0);

[samuong, 2016/12/21 00:02:26]

If a WebDriver client sends a command to synthesize a pointer action, and sets
the mouse index to something other than 0, we need to catch this somehow.

If this function is the place where this check is supposed to happen, then we
wouldn't want a DCHECK here. Should we just return false instead?

[lanwei, 2016/12/21 20:01:14]

Because we do not use the index for mouse type, so I use DCHECK as a warning.
But since we will put this requirement in the doc, and do not support
multi-mouse devices, return false is better.

Done.

   if (params.pointer_action_type() ==
       SyntheticPointerActionParams::PointerActionType::NOT_INITIALIZED) {
     return false;