Add User Actions and adding more details to UMA metrics for overscroll navigation

content/browser/web_contents/aura/overscroll_window_animation.h

Index: content/browser/web_contents/aura/overscroll_window_animation.h
diff --git a/content/browser/web_contents/aura/overscroll_window_animation.h b/content/browser/web_contents/aura/overscroll_window_animation.h
index f19e5f8bcc71a87ad29859f747024c1de51b3f2c..e41275511fd84e0bea3d9254aab6acad1d010274 100644
--- a/content/browser/web_contents/aura/overscroll_window_animation.h
+++ b/content/browser/web_contents/aura/overscroll_window_animation.h
@@ -77,12 +77,19 @@ class CONTENT_EXPORT OverscrollWindowAnimation
   // Returns true if we are currently animating.
   bool is_active() const { return !!slide_window_; }
 
+  OverscrollSource overscroll_source() { return overscroll_source_; }
+
+  void SetOverscrollSourceForTesting(OverscrollSource source) {
+    overscroll_source_ = source;
+  }
+
   // OverscrollControllerDelegate:
   gfx::Rect GetVisibleBounds() const override;
   bool OnOverscrollUpdate(float delta_x, float delta_y) override;
   void OnOverscrollComplete(OverscrollMode overscroll_mode) override;
   void OnOverscrollModeChange(OverscrollMode old_mode,
-                              OverscrollMode new_mode) override;
+                              OverscrollMode new_mode,
+                              OverscrollSource source) override;
 
  private:
   // Cancels the slide, animating the front and back window to their original
@@ -119,6 +126,11 @@ class CONTENT_EXPORT OverscrollWindowAnimation
   // The current animation direction.
   Direction direction_;
 
+  // OverscrollSource of the current overscroll gesture. Updated when the new
+  // overscroll gesture starts, before CreateFront/BackWindow callback is called
+  // on the delegate.
+  OverscrollSource overscroll_source_ = OverscrollSource::NONE;
+
   // Indicates if the current slide has been cancelled. True while the cancel
   // animation is in progress.
   bool overscroll_cancelled_;