Use pure virtual functions at TransportFlowControlBase

src/core/ext/transport/chttp2/transport/flow_control.h

@@ -140,8 +140,7 @@ class FlowControlTrace {
 };
 
 // Fat interface with all methods a flow control implementation needs to
-// support. gRPC C Core does not support pure virtual functions, so instead
-// we abort in any methods which require implementation in the base class.
+// support.
 class TransportFlowControlBase {
  public:
   TransportFlowControlBase() {}
@@ -149,30 +148,30 @@ class TransportFlowControlBase {
 
   // Is flow control enabled? This is needed in other codepaths like the checks
   // in parsing and in writing.
-  virtual bool flow_control_enabled() const { abort(); }
+  virtual bool flow_control_enabled() const = 0;
 
   // Called to check if the transport needs to send a WINDOW_UPDATE frame
-  virtual uint32_t MaybeSendUpdate(bool /* writing_anyway */) { abort(); }
+  virtual uint32_t MaybeSendUpdate(bool /* writing_anyway */) = 0;
 
   // Using the protected members, returns and Action to be taken by the
   // tranport.
-  virtual FlowControlAction MakeAction() { abort(); }
+  virtual FlowControlAction MakeAction() = 0;
 
   // Using the protected members, returns and Action to be taken by the
   // tranport. Also checks for updates to our BDP estimate and acts
   // accordingly.
-  virtual FlowControlAction PeriodicUpdate() { abort(); }
+  virtual FlowControlAction PeriodicUpdate() = 0;
 
   // Called to do bookkeeping when a stream owned by this transport sends
   // data on the wire
-  virtual void StreamSentData(int64_t /* size */) { abort(); }
+  virtual void StreamSentData(int64_t /* size */) = 0;
 
   // Called to do bookkeeping when a stream owned by this transport receives
   // data from the wire. Also does error checking for frame size.
-  virtual grpc_error* RecvData(int64_t /* incoming_frame_size */) { abort(); }
+  virtual grpc_error* RecvData(int64_t /* incoming_frame_size */) = 0;
 
   // Called to do bookkeeping when we receive a WINDOW_UPDATE frame.
-  virtual void RecvUpdate(uint32_t /* size */) { abort(); }
+  virtual void RecvUpdate(uint32_t /* size */) = 0;
 
   // Returns the BdpEstimator held by this object. Caller is responsible for
   // checking for nullptr. TODO(ncteisen): consider fully encapsulating all