Improve const-correctness for WritableStream classes

Make const accessors return const pointers. Mark more method arguments
as const.

BUG=902633

Change-Id: I4d743be2ab56af4d3a9be493ba4b322d5ef40b41
Reviewed-on: https://chromium-review.googlesource.com/c/1488396Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635920}

third_party/blink/renderer/core/streams/writable_stream_default_controller.cc

@@ -343,7 +343,7 @@ double WritableStreamDefaultController::GetChunkSize(
 }
 
 double WritableStreamDefaultController::GetDesiredSize(
-    WritableStreamDefaultController* controller) {
+    const WritableStreamDefaultController* controller) {
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-get-desired-size
   //  1. Return controller.[[strategyHWM]] − controller.[[queueTotalSize]].
   return controller->strategy_high_water_mark_ -
@@ -658,7 +658,7 @@ void WritableStreamDefaultController::ProcessWrite(
 }
 
 bool WritableStreamDefaultController::GetBackpressure(
-    WritableStreamDefaultController* controller) {
+    const WritableStreamDefaultController* controller) {
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-get-backpressure
   //  1. Let desiredSize be ! WritableStreamDefaultControllerGetDesiredSize(
   //     controller).

third_party/blink/renderer/core/streams/writable_stream_default_controller.h

@@ -73,12 +73,13 @@ class WritableStreamDefaultController final : public ScriptWrappable {
   static void Close(ScriptState*, WritableStreamDefaultController*);
 
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-get-chunk-size
+  // May error the stream as a side-effect.
   static double GetChunkSize(ScriptState*,
                              WritableStreamDefaultController*,
                              v8::Local<v8::Value> chunk);
 
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-get-desired-size
-  static double GetDesiredSize(WritableStreamDefaultController*);
+  static double GetDesiredSize(const WritableStreamDefaultController*);
 
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-write
   static void Write(ScriptState*,
@@ -113,7 +114,7 @@ class WritableStreamDefaultController final : public ScriptWrappable {
                            v8::Local<v8::Value> chunk);
 
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-get-backpressure
-  static bool GetBackpressure(WritableStreamDefaultController*);
+  static bool GetBackpressure(const WritableStreamDefaultController*);
 
   // https://streams.spec.whatwg.org/#writable-stream-default-controller-error
   static void Error(ScriptState*,

third_party/blink/renderer/core/streams/writable_stream_default_writer.h

@@ -77,8 +77,8 @@ class WritableStreamDefaultWriter final : public ScriptWrappable {
   // not appear in the standard.
   //
 
-  StreamPromiseResolver* ClosedPromise() const { return closed_promise_; }
-  StreamPromiseResolver* ReadyPromise() const { return ready_promise_; }
+  StreamPromiseResolver* ClosedPromise() { return closed_promise_; }
+  StreamPromiseResolver* ReadyPromise() { return ready_promise_; }
 
   void SetReadyPromise(StreamPromiseResolver*);
 

third_party/blink/renderer/core/streams/writable_stream_native.cc

@@ -777,7 +777,7 @@ void WritableStreamNative::UpdateBackpressure(ScriptState* script_state,
   DCHECK(!CloseQueuedOrInFlight(stream));
 
   //  3. Let writer be stream.[[writer]].
-  const auto writer = stream->writer_;
+  WritableStreamDefaultWriter* writer = stream->writer_;
 
   //  4. If writer is not undefined and backpressure is not
   //     stream.[[backpressure]],

third_party/blink/renderer/core/streams/writable_stream_native.h

@@ -154,7 +154,7 @@ class CORE_EXPORT WritableStreamNative : public WritableStream {
 
   bool HasBackpressure() const { return has_backpressure_; }
 
-  StreamPromiseResolver* InFlightWriteRequest() const {
+  const StreamPromiseResolver* InFlightWriteRequest() const {
     return in_flight_write_request_;
   }
 
@@ -164,11 +164,14 @@ class CORE_EXPORT WritableStreamNative : public WritableStream {
 
   v8::Local<v8::Value> GetStoredError(v8::Isolate*) const;
 
-  WritableStreamDefaultController* Controller() const {
+  WritableStreamDefaultController* Controller() {
+    return writable_stream_controller_;
+  }
+  const WritableStreamDefaultController* Controller() const {
     return writable_stream_controller_;
   }
 
-  WritableStreamDefaultWriter* Writer() const { return writer_; }
+  const WritableStreamDefaultWriter* Writer() const { return writer_; }
 
   void SetCloseRequest(StreamPromiseResolver*);
   void SetController(WritableStreamDefaultController*);