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diff --git a/gfx/layers/apz/util/ScrollInputMethods.h b/gfx/layers/apz/util/ScrollInputMethods.h
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+++ b/gfx/layers/apz/util/ScrollInputMethods.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_ScrollInputMethods_h
+#define mozilla_layers_ScrollInputMethods_h
+
+namespace mozilla {
+namespace layers {
+
+/**
+ * An enumeration that lists various input methods used to trigger scrolling.
+ * Used as the values for the SCROLL_INPUT_METHODS telemetry histogram.
+ */
+enum class ScrollInputMethod {
+
+  // === Driven by APZ ===
+
+  ApzTouch,          // touch events
+  ApzWheelPixel,     // wheel events, pixel scrolling mode
+  ApzWheelLine,      // wheel events, line scrolling mode
+  ApzWheelPage,      // wheel events, page scrolling mode
+  ApzPanGesture,     // pan gesture events (generally triggered by trackpad)
+  ApzScrollbarDrag,  // dragging the scrollbar
+
+  // === Driven by the main thread ===
+
+  // Keyboard
+  MainThreadScrollLine,       // line scrolling
+                              // (generally triggered by up/down arrow keys)
+  MainThreadScrollCharacter,  // character scrolling
+                              // (generally triggered by left/right arrow keys)
+  MainThreadScrollPage,       // page scrolling
+                              // (generally triggered by PageUp/PageDown keys)
+  MainThreadCompleteScroll,   // scrolling to the end of the scroll range
+                              // (generally triggered by Home/End keys)
+  MainThreadScrollCaretIntoView,  // scrolling to bring the caret into view
+                                  // after moving the caret via the keyboard
+
+  // Touch
+  MainThreadTouch,            // touch events
+
+  // Scrollbar
+  MainThreadScrollbarDrag,         // dragging the scrollbar
+  MainThreadScrollbarButtonClick,  // clicking the buttons at the ends of the
+                                   // scrollback track
+  MainThreadScrollbarTrackClick,   // clicking the scrollbar track above or
+                                   // below the thumb
+
+  // Autoscrolling
+  MainThreadAutoscrolling,    // autoscrolling
+
+  // New input methods can be added at the end, up to a maximum of 64.
+  // They should only be added at the end, to preserve the numerical values
+  // of the existing enumerators.
+};
+
+} // namespace layers
+} // namespace mozilla
+
+#endif /* mozilla_layers_ScrollInputMethods_h */