Put all reasons in MainThreadScrollingReason into one enum

cc/input/main_thread_scrolling_reason.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_INPUT_MAIN_THREAD_SCROLLING_REASON_H_
 #define CC_INPUT_MAIN_THREAD_SCROLLING_REASON_H_
 
 #include <string>
 
 #include "base/trace_event/trace_event_argument.h"
 
 namespace cc {
 
 // Ensure this stays in sync with MainThreadScrollingReason in histograms.xml.
 // When adding a new MainThreadScrollingReason, make sure the corresponding
 // [MainThread/Compositor]CanSetScrollReasons function is also updated.
 struct MainThreadScrollingReason {
-  // Non-transient scrolling reasons.
-  enum : uint32_t { kNotScrollingOnMain = 0 };
-  enum : uint32_t { kHasBackgroundAttachmentFixedObjects = 1 << 0 };
-  enum : uint32_t { kHasNonLayerViewportConstrainedObjects = 1 << 1 };
-  enum : uint32_t { kThreadedScrollingDisabled = 1 << 2 };
-  enum : uint32_t { kScrollbarScrolling = 1 << 3 };
-  enum : uint32_t { kPageOverlay = 1 << 4 };
-  // This bit is set when any of the other main thread scrolling reasons cause
-  // an input event to be handled on the main thread, and the main thread
-  // blink::ScrollAnimator is in the middle of running a scroll offset
-  // animation. Note that a scroll handled by the main thread can result in an
-  // animation running on the main thread or on the compositor thread.
-  enum : uint32_t { kHandlingScrollFromMainThread = 1 << 13 };
-  enum : uint32_t { kCustomScrollbarScrolling = 1 << 15 };
+  enum : uint32_t {
+    // Non-transient scrolling reasons.
+    kNotScrollingOnMain = 0,
+    kHasBackgroundAttachmentFixedObjects = 1 << 0,
+    kHasNonLayerViewportConstrainedObjects = 1 << 1,
+    kThreadedScrollingDisabled = 1 << 2,
+    kScrollbarScrolling = 1 << 3,
+    kPageOverlay = 1 << 4,
 
-  // Transient scrolling reasons. These are computed for each scroll begin.
-  enum : uint32_t { kNonFastScrollableRegion = 1 << 5 };
-  enum : uint32_t { kFailedHitTest = 1 << 7 };
-  enum : uint32_t { kNoScrollingLayer = 1 << 8 };
-  enum : uint32_t { kNotScrollable = 1 << 9 };
-  enum : uint32_t { kContinuingMainThreadScroll = 1 << 10 };
-  enum : uint32_t { kNonInvertibleTransform = 1 << 11 };
-  enum : uint32_t { kPageBasedScrolling = 1 << 12 };
+    // This bit is set when any of the other main thread scrolling reasons cause
+    // an input event to be handled on the main thread, and the main thread
+    // blink::ScrollAnimator is in the middle of running a scroll offset
+    // animation. Note that a scroll handled by the main thread can result in an
+    // animation running on the main thread or on the compositor thread.
+    kHandlingScrollFromMainThread = 1 << 13,
+    kCustomScrollbarScrolling = 1 << 15,
 
-  // The number of flags in this struct (excluding itself).
-  enum : uint32_t { kMainThreadScrollingReasonCount = 17 };
+    // Transient scrolling reasons. These are computed for each scroll begin.
+    kNonFastScrollableRegion = 1 << 5,
+    kFailedHitTest = 1 << 7,
+    kNoScrollingLayer = 1 << 8,
+    kNotScrollable = 1 << 9,
+    kContinuingMainThreadScroll = 1 << 10,
+    kNonInvertibleTransform = 1 << 11,
+    kPageBasedScrolling = 1 << 12,
+
+    // The number of flags in this struct (excluding itself).
+    kMainThreadScrollingReasonCount = 17,
+  };
 
   // Returns true if the given MainThreadScrollingReason can be set by the main
   // thread.
   static bool MainThreadCanSetScrollReasons(uint32_t reasons) {
     uint32_t reasons_set_by_main_thread =
         kNotScrollingOnMain | kHasBackgroundAttachmentFixedObjects |
         kHasNonLayerViewportConstrainedObjects | kThreadedScrollingDisabled |
         kScrollbarScrolling | kPageOverlay | kHandlingScrollFromMainThread |
         kCustomScrollbarScrolling;
     return (reasons & reasons_set_by_main_thread) == reasons;
@@ skipping 56 matching lines @@
       tracedValue->AppendString("Non-invertible transform");
     if (reasons & MainThreadScrollingReason::kPageBasedScrolling)
       tracedValue->AppendString("Page-based scrolling");
     tracedValue->EndArray();
   }
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_MAIN_THREAD_SCROLLING_REASON_H_