Add code to collect crash data for https://crbug.com/592319.

content/browser/renderer_host/render_widget_host_input_event_router.cc

Index: content/browser/renderer_host/render_widget_host_input_event_router.cc
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.cc b/content/browser/renderer_host/render_widget_host_input_event_router.cc
index 0343bd97aaba02d54a0b59a37886b6cb09b954fa..0b4af7622d2939403678a4aca5ba76245b3219b6 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.cc
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.cc
@@ -4,6 +4,7 @@
 
 #include "content/browser/renderer_host/render_widget_host_input_event_router.h"
 
+#include "base/debug/dump_without_crashing.h"
 #include "cc/quads/surface_draw_quad.h"
 #include "cc/surfaces/surface_id_allocator.h"
 #include "cc/surfaces/surface_manager.h"
@@ -90,7 +91,16 @@ bool RenderWidgetHostInputEventRouter::HittestDelegate::AcceptHitTarget(
 RenderWidgetHostInputEventRouter::RenderWidgetHostInputEventRouter()
     : touch_target_(nullptr),
       gesture_target_(nullptr),
-      active_touches_(0) {}
+      active_touches_(0),
+      number_of_gesture_targets_enqueued_(0),
+      number_of_gesture_targets_dequeued_(0),
+      last_gesture_event_index_(0),
+      last_touch_event_index_(0) {
+  for (unsigned i = 0; i < kNumLastEventTypes; ++i) {
+    last_gesture_event_types_[i] = blink::WebInputEvent::Undefined;
+    last_touch_event_types_[i] = blink::WebInputEvent::Undefined;
+  }
+}
 
 RenderWidgetHostInputEventRouter::~RenderWidgetHostInputEventRouter() {
   // We may be destroyed before some of the owners in the map, so we must
@@ -170,13 +180,28 @@ void RenderWidgetHostInputEventRouter::RouteGestureEvent(
   // GestureTapDown is sent to the previous target, in case it is still in a
   // fling.
   if (event->type == blink::WebInputEvent::GestureTapDown) {
-    DCHECK(!gesture_target_queue_.empty());
+    if (gesture_target_queue_.empty()) {
+      // Collect data to assist debugging https://crbug.com/592319.
+      // We'll assume for now if there's no target that we should just ignore
+      // the event.
+      LOG(ERROR) << "Gesture sequence start detected with no target available.";
+      base::debug::DumpWithoutCrashing();
+      return;
+    }
+
     const GestureTargetData& data = gesture_target_queue_.front();
     gesture_target_ = data.target;
     gesture_delta_ = data.delta;
     gesture_target_queue_.pop_front();
+    // Code to assist debugging https://crbug.com/592319.
+    number_of_gesture_targets_dequeued_++;
   }
 
+  // Code to assist debugging https://crbug.com/592319.
+  last_gesture_event_types_[last_gesture_event_index_] = event->type;
+  last_gesture_event_index_ =
+      (last_gesture_event_index_ + 1) % kNumLastEventTypes;

[tdresser, 2016/03/09 19:53:45]

Based on the code here, isn't last_gesture_event_index actually
next_gesture_event_index?

[wjmaclean, 2016/03/09 21:28:31]

Done.

+
   if (!gesture_target_)
     return;
 
@@ -189,6 +214,11 @@ void RenderWidgetHostInputEventRouter::RouteTouchEvent(
     RenderWidgetHostViewBase* root_view,
     blink::WebTouchEvent* event,
     const ui::LatencyInfo& latency) {
+  // Code to assist debugging https://crbug.com/592319.
+  last_touch_event_types_[last_touch_event_index_] = event->type;
+  last_touch_event_index_ =
+      (last_touch_event_index_ + 1) % kNumLastEventTypes;

[tdresser, 2016/03/09 19:53:45]

Looks like this is next_touch_event_index_.

[wjmaclean, 2016/03/09 21:28:31]

Done.

+
   switch (event->type) {
     case blink::WebInputEvent::TouchStart: {
       if (!active_touches_) {
@@ -208,6 +238,8 @@ void RenderWidgetHostInputEventRouter::RouteTouchEvent(
         // for the duration of the sequence.
         touch_delta_ = transformed_point - original_point;
         gesture_target_queue_.emplace_back(touch_target_, touch_delta_);
+        // Code to assist debugging https://crbug.com/592319.
+        number_of_gesture_targets_enqueued_++;
 
         if (!touch_target_)
           return;