Add a BrowserViewRenderer unittest for compositor switch logic

android_webview/browser/browser_view_renderer.h

 // Copyright (c) 2013 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 ANDROID_WEBVIEW_BROWSER_BROWSER_VIEW_RENDERER_H_
 #define ANDROID_WEBVIEW_BROWSER_BROWSER_VIEW_RENDERER_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 120 matching lines @@
                      const gfx::Vector2dF& current_fling_velocity) override;
 
   // CompositorFrameProducer overrides
   void OnParentDrawConstraintsUpdated(
       CompositorFrameConsumer* compositor_frame_consumer) override;
   void RemoveCompositorFrameConsumer(
       CompositorFrameConsumer* compositor_frame_consumer) override;
 
   void SetActiveCompositorID(const CompositorID& compositor_id);
 
+  // Visible for testing.
+  content::SynchronousCompositor* GetActiveCompositorForTesting() const {
+    return compositor_;
+  }
+
  private:
   void SetTotalRootLayerScrollOffset(const gfx::Vector2dF& new_value_dip);
   bool CanOnDraw();
   bool CompositeSW(SkCanvas* canvas);
   std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
   RootLayerStateAsValue(const gfx::Vector2dF& total_scroll_offset_dip,
                         const gfx::SizeF& scrollable_size_dip);
 
   void ReturnUnusedResource(std::unique_ptr<ChildFrame> frame);
   void ReturnResourceFromParent(
@@ skipping 64 matching lines @@
   gfx::Vector2dF overscroll_rounding_error_;
 
   ParentCompositorDrawConstraints external_draw_constraints_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserViewRenderer);
 };
 
 }  // namespace android_webview
 
 #endif  // ANDROID_WEBVIEW_BROWSER_BROWSER_VIEW_RENDERER_H_