Fix flaky SyntheticMouseEventTest.MouseEventAck

Devtools was not correctly handling input that is not generated by itself
and invoking callbacks when the input wasn't actually processed.

Add a modifier indicating content was injected using the debugger so that
we can then query for that to determine if we should release the event.
This is a stop gap solution until we can actually bind callbacks into the
sending of events and devtools wouldn't need its own queues of callbacks.

BUG=789869

Change-Id: I2b56e8ebf4921b48bd4d35dee2226d7cb780cb94
Reviewed-on: https://chromium-review.googlesource.com/804357
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521454}

content/browser/devtools/protocol/devtools_protocol_browsertest.cc

@@ -582,7 +582,7 @@ IN_PROC_BROWSER_TEST_F(SyntheticKeyEventTest, KeyboardEventAck) {
   EXPECT_EQ(3u, result_ids_.size());
 }
 
-IN_PROC_BROWSER_TEST_F(SyntheticMouseEventTest, DISABLED_MouseEventAck) {
+IN_PROC_BROWSER_TEST_F(SyntheticMouseEventTest, MouseEventAck) {
   NavigateToURLBlockUntilNavigationsComplete(shell(), GURL("about:blank"), 1);
   Attach();
   ASSERT_TRUE(content::ExecuteScript(

content/browser/devtools/protocol/input_handler.cc

@@ -66,7 +66,7 @@ int GetEventModifiers(int modifiers,
                       bool auto_repeat,
                       bool is_keypad,
                       int location) {
-  int result = 0;
+  int result = blink::WebInputEvent::kFromDebugger;
   if (auto_repeat)
     result |= blink::WebInputEvent::kIsAutoRepeat;
   if (is_keypad)
@@ -293,6 +293,9 @@ void InputHandler::OnInputEvent(const blink::WebInputEvent& event) {
 void InputHandler::OnInputEventAck(InputEventAckSource source,
                                    InputEventAckState state,
                                    const blink::WebInputEvent& event) {
+  if ((event.GetModifiers() & blink::WebInputEvent::kFromDebugger) == 0)
+    return;
+
   if (blink::WebInputEvent::IsKeyboardEventType(event.GetType()) &&
       !pending_key_callbacks_.empty()) {
     pending_key_callbacks_.front()->sendSuccess();

third_party/WebKit/public/platform/WebInputEvent.h

@@ -246,6 +246,11 @@ class WebInputEvent {
     // not actual physical movement of the pointer
     kRelativeMotionEvent = 1 << 22,
 
+    // Indication this event was injected by the devtools.
+    // TODO(dtapuska): Remove this flag once we are able to bind callbacks
+    // in event sending.
+    kFromDebugger = 1 << 23,
+
     // The set of non-stateful modifiers that specifically change the
     // interpretation of the key being pressed. For example; IsLeft,
     // IsRight, IsComposing don't change the meaning of the key