aw: Abstract pure virtual functions in SynchronousCompositorClient

These two functions need to be abstract.

Bug: 1004544
Change-Id: I893a47747333d6e39a6855cb7e3627a0ea6a8e00
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829874
Auto-Submit: Shimi Zhang <ctzsm@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701530}

content/public/browser/android/synchronous_compositor_client.h

@@ -33,14 +33,14 @@ class SynchronousCompositorClient {
   // compositor thread, and open for business. |process_id| and |routing_id|
   // belong to the RVH that owns the compositor.
   virtual void DidInitializeCompositor(SynchronousCompositor* compositor,
-                                       const viz::FrameSinkId& id);
+                                       const viz::FrameSinkId& id) = 0;
 
   // Indication to the client that |compositor| is going out of scope, and
   // must not be accessed within or after this call.
   // NOTE if the client goes away before the compositor it must call
   // SynchronousCompositor::SetClient(nullptr) to release the back pointer.
   virtual void DidDestroyCompositor(SynchronousCompositor* compositor,
-                                    const viz::FrameSinkId& id);
+                                    const viz::FrameSinkId& id) = 0;
 
   virtual void UpdateRootLayerState(SynchronousCompositor* compositor,
                                     const gfx::Vector2dF& total_scroll_offset,