Raw Clipboard: Remove no-op thread hop.

This thread hop isn't necessary, because raw data doesn't require
decoding.

Bug: 897289
Change-Id: Id3c75b2a0dcde2b6950d3a1a3085db6e73ffd273
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2406695Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Auto-Submit: Darwin Huang <huangdarwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824218}

third_party/blink/renderer/modules/clipboard/clipboard_writer.cc

@@ -209,6 +209,7 @@ class ClipboardSvgWriter final : public ClipboardWriter {
     promise_->CompleteWriteRepresentation();
   }
 };
+
 // Writes a blob with arbitrary, unsanitized content to the System Clipboard.
 class ClipboardRawDataWriter final : public ClipboardWriter {
  public:
@@ -223,25 +224,14 @@ class ClipboardRawDataWriter final : public ClipboardWriter {
                   DOMArrayBuffer* raw_data) override {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
-    worker_pool::PostTask(
-        FROM_HERE,
-        CrossThreadBindOnce(&ClipboardRawDataWriter::DecodeOnBackgroundThread,
-                            WrapCrossThreadPersistent(this), task_runner,
-                            WrapCrossThreadPersistent(raw_data)));
+    // Raw Data is written directly, and doesn't require decoding.
+    Write(raw_data);
   }
 
-  // Unfortunately, in order to use the same ClipboardWriter base,
-  // ClipboardRawDataWriter does need to have these extra 2 thread hops.
   void DecodeOnBackgroundThread(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
       DOMArrayBuffer* raw_data) override {
-    DCHECK(!IsMainThread());
-
-    PostCrossThreadTask(
-        *task_runner, FROM_HERE,
-        CrossThreadBindOnce(&ClipboardRawDataWriter::Write,
-                            WrapCrossThreadPersistent(this),
-                            WrapCrossThreadPersistent(raw_data)));
+    NOTREACHED() << "Raw Data doesn't require decoding.";
   }
 
   void Write(DOMArrayBuffer* raw_data) {

third_party/blink/renderer/modules/clipboard/clipboard_writer.h

@@ -58,6 +58,8 @@ class ClipboardWriter : public GarbageCollected<ClipboardWriter>,
   ClipboardWriter(RawSystemClipboard* raw_system_clipboard,
                   ClipboardPromise* promise);
 
+  // Decodes and writes `raw_data`. Decoding is done off the main thread
+  // whenever possible, by calling DecodeOnBackgroundThread.
   virtual void StartWrite(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
       DOMArrayBuffer* raw_data) = 0;