blink: Make WebMainThreadScrollingReason wrap the cc enum.

This moves the WebMainThreadScrollingReason from public/platform/ to
platform/scroll/, as it is no longer used in the WebLayer API
explicitly, and renames it to just MainThreadScrollingReason. We change
the type to be an alias for the cc type instead of maintaining static
asserts that they match.

Depends on: https://codereview.chromium.org/1604053002/
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1602773006

Cr-Commit-Position: refs/heads/master@{#371151}

1 files changed, 2 insertions, 6 deletions

diff --git a/cc/input/main_thread_scrolling_reason.h b/cc/input/main_thread_scrolling_reason.h
index 6ab823c..4de70f7 100644
--- a/cc/input/main_thread_scrolling_reason.h
+++ b/cc/input/main_thread_scrolling_reason.h
@@ -7,11 +7,7 @@
 
 namespace cc {
 
-// Ensure this stays in sync with MainThreadScrollingReason in histograms.xml,
-// and that this extends ScrollingCoordinator::MainThreadScrollingReason.
-// ScrollingCoordinator::MainThreadScrollingReason contains the flags
-// which are associated with a layer. The flags only contained in
-// MainThreadScrollingReason are computed for each scroll begin.
+// Ensure this stays in sync with MainThreadScrollingReason in histograms.xml.
 struct MainThreadScrollingReason {
   // Non-transient scrolling reasons.
   enum : uint32_t { kNotScrollingOnMain = 0 };
@@ -22,7 +18,7 @@ struct MainThreadScrollingReason {
   enum : uint32_t { kPageOverlay = 1 << 4 };
   enum : uint32_t { kMaxNonTransientScrollingReason = kPageOverlay };
 
-  // Transient scrolling reasons.
+  // 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 };