Remove cc's MainThreadScrollingReason::kEventHandlers

cc/input/main_thread_scrolling_reason.h

Index: cc/input/main_thread_scrolling_reason.h
diff --git a/cc/input/main_thread_scrolling_reason.h b/cc/input/main_thread_scrolling_reason.h
index 2d45a4229645b6fa538768593c173027aca57b1a..855002f37e26671d0bff223ba518548374c0397d 100644
--- a/cc/input/main_thread_scrolling_reason.h
+++ b/cc/input/main_thread_scrolling_reason.h
@@ -32,7 +32,6 @@ struct MainThreadScrollingReason {
 
   // Transient scrolling reasons. These are computed for each scroll begin.
   enum : uint32_t { kNonFastScrollableRegion = 1 << 5 };
-  enum : uint32_t { kEventHandlers = 1 << 6 };
   enum : uint32_t { kFailedHitTest = 1 << 7 };
   enum : uint32_t { kNoScrollingLayer = 1 << 8 };
   enum : uint32_t { kNotScrollable = 1 << 9 };
@@ -41,7 +40,7 @@ struct MainThreadScrollingReason {
   enum : uint32_t { kPageBasedScrolling = 1 << 12 };
 
   // The number of flags in this struct (excluding itself).
-  enum : uint32_t { kMainThreadScrollingReasonCount = 17 };
+  enum : uint32_t { kMainThreadScrollingReasonCount = 16 };

[dtapuska, 2016/09/22 13:36:44]

I'm not sure this is right. I think it is supposed to be size + 1.

The max shift size is 15 from looking at the code. So the size is 16. And then
this code uses it
https://cs.chromium.org/chromium/src/ui/events/blink/input_handler_proxy.cc?q...

I'm not saying the usage is right. But just trying to understand the motivation
of this change for this line.

[pdr., 2016/09/22 19:57:40]

Good catch. This is pretty confusing... if the max is 15 then the count should
be 16 (zero indexed) but you're right that the usage assumes otherwise. I've
backed out this change so that this patch is just the removal of an unused enum.

 
   // Returns true if the given MainThreadScrollingReason can be set by the main
   // thread.
@@ -58,9 +57,9 @@ struct MainThreadScrollingReason {
   // compositor.
   static bool CompositorCanSetScrollReasons(uint32_t reasons) {
     uint32_t reasons_set_by_compositor =
-        kNonFastScrollableRegion | kEventHandlers | kFailedHitTest |
-        kNoScrollingLayer | kNotScrollable | kContinuingMainThreadScroll |
-        kNonInvertibleTransform | kPageBasedScrolling;
+        kNonFastScrollableRegion | kFailedHitTest | kNoScrollingLayer |
+        kNotScrollable | kContinuingMainThreadScroll | kNonInvertibleTransform |
+        kPageBasedScrolling;
     return (reasons & reasons_set_by_compositor) == reasons;
   }
 
@@ -99,8 +98,6 @@ struct MainThreadScrollingReason {
     // Transient scrolling reasons.
     if (reasons & MainThreadScrollingReason::kNonFastScrollableRegion)
       tracedValue->AppendString("Non fast scrollable region");
-    if (reasons & MainThreadScrollingReason::kEventHandlers)
-      tracedValue->AppendString("Event handlers");
     if (reasons & MainThreadScrollingReason::kFailedHitTest)
       tracedValue->AppendString("Failed hit test");
     if (reasons & MainThreadScrollingReason::kNoScrollingLayer)