Clipboard API: Add early returns and comments.

Add early returns when returning to the main thread, to ensure the
ExecutionContext or LocalFrame is always valid before use.
Also, add some comments for consistency between subclasses.

Change-Id: I6abe00c90405c44214a45c8b5d02e070db767956
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551304
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Auto-Submit: Darwin Huang <huangdarwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836960}

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

@@ -15,12 +15,12 @@
 #include "third_party/blink/renderer/core/fileapi/blob.h"
 #include "third_party/blink/renderer/modules/clipboard/clipboard_item.h"
 #include "third_party/blink/renderer/modules/clipboard/clipboard_reader.h"
-#include "third_party/blink/renderer/modules/clipboard/clipboard_writer.h"
 #include "third_party/blink/renderer/platform/mojo/heap_mojo_remote.h"
 #include "third_party/blink/renderer/platform/mojo/heap_mojo_wrapper_mode.h"
 
 namespace blink {
 
+class ClipboardWriter;
 class ScriptPromiseResolver;
 class LocalFrame;
 class ExecutionContext;

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

@@ -221,7 +221,7 @@ class ClipboardHtmlReader final : public ClipboardReader {
   }
 };
 
-// Reads SVG from the System Clipboard as a Blob with image/svg content.
+// Reads SVG from the System Clipboard as a Blob with image/svg+xml content.
 class ClipboardSvgReader final : public ClipboardReader {
  public:
   ClipboardSvgReader(SystemClipboard* system_clipboard,

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

@@ -16,7 +16,6 @@
 #include "third_party/blink/renderer/core/fileapi/file_reader_loader.h"
 #include "third_party/blink/renderer/core/frame/local_frame.h"
 #include "third_party/blink/renderer/core/imagebitmap/image_bitmap.h"
-#include "third_party/blink/renderer/modules/clipboard/clipboard_promise.h"
 #include "third_party/blink/renderer/platform/image-decoders/image_decoder.h"
 #include "third_party/blink/renderer/platform/runtime_enabled_features.h"
 #include "third_party/blink/renderer/platform/scheduler/public/post_cross_thread_task.h"
@@ -74,6 +73,8 @@ class ClipboardImageWriter final : public ClipboardWriter {
       promise_->RejectFromReadOrDecodeFailure();
       return;
     }
+    if (!promise_->GetLocalFrame())
+      return;
     SkBitmap bitmap;
     image->asLegacyBitmap(&bitmap);
     system_clipboard()->WriteImage(std::move(bitmap));
@@ -118,12 +119,15 @@ class ClipboardTextWriter final : public ClipboardWriter {
   }
   void Write(const String& text) {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+    if (!promise_->GetLocalFrame())
+      return;
     system_clipboard()->WritePlainText(text);
 
     promise_->CompleteWriteRepresentation();
   }
 };
 
+// Writes a blob with text/html content to the System Clipboard.
 class ClipboardHtmlWriter final : public ClipboardWriter {
  public:
   ClipboardHtmlWriter(SystemClipboard* system_clipboard,
@@ -137,8 +141,10 @@ class ClipboardHtmlWriter final : public ClipboardWriter {
       scoped_refptr<base::SingleThreadTaskRunner> task_runner) override {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
-    promise_->GetExecutionContext()->CountUse(
-        WebFeature::kHtmlClipboardApiWrite);
+    auto* execution_context = promise_->GetExecutionContext();
+    if (!execution_context)
+      return;
+    execution_context->CountUse(WebFeature::kHtmlClipboardApiWrite);
 
     String html_string =
         String::FromUTF8(reinterpret_cast<const LChar*>(html_data->Data()),
@@ -150,7 +156,10 @@ class ClipboardHtmlWriter final : public ClipboardWriter {
     unsigned fragment_start = 0;
     unsigned fragment_end = html_string.length();
 
-    Document* document = promise_->GetLocalFrame()->GetDocument();
+    LocalFrame* local_frame = promise_->GetLocalFrame();
+    if (!local_frame)
+      return;
+    Document* document = local_frame->GetDocument();
     DocumentFragment* fragment = CreateSanitizedFragmentFromMarkupWithContext(
         *document, html_string, fragment_start, fragment_end, url);
     String sanitized_html =
@@ -165,6 +174,7 @@ class ClipboardHtmlWriter final : public ClipboardWriter {
   }
 };
 
+// Writes a blob with image/svg+xml content to the System Clipboard.
 class ClipboardSvgWriter final : public ClipboardWriter {
  public:
   ClipboardSvgWriter(SystemClipboard* system_clipboard,
@@ -188,7 +198,10 @@ class ClipboardSvgWriter final : public ClipboardWriter {
     unsigned fragment_start = 0;
     unsigned fragment_end = svg_string.length();
 
-    Document* document = promise_->GetLocalFrame()->GetDocument();
+    LocalFrame* local_frame = promise_->GetLocalFrame();
+    if (!local_frame)
+      return;
+    Document* document = local_frame->GetDocument();
     DocumentFragment* fragment = CreateSanitizedFragmentFromMarkupWithContext(
         *document, svg_string, fragment_start, fragment_end, url);
     String sanitized_svg =
@@ -235,6 +248,8 @@ class ClipboardRawDataWriter final : public ClipboardWriter {
     mojo_base::BigBuffer buffer(std::vector<uint8_t>(
         raw_data_pointer, raw_data_pointer + raw_data->ByteLength()));
 
+    if (!promise_->GetLocalFrame())
+      return;
     raw_system_clipboard()->Write(mime_type_, std::move(buffer));
 
     promise_->CompleteWriteRepresentation();

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

@@ -8,13 +8,13 @@
 #include "base/sequence_checker.h"
 #include "third_party/blink/renderer/core/fileapi/blob.h"
 #include "third_party/blink/renderer/core/fileapi/file_reader_loader_client.h"
+#include "third_party/blink/renderer/modules/clipboard/clipboard_promise.h"
 #include "third_party/blink/renderer/platform/heap/heap.h"
 #include "third_party/blink/renderer/platform/heap/self_keep_alive.h"
 #include "third_party/skia/include/core/SkImage.h"
 
 namespace blink {
 
-class ClipboardPromise;
 class FileReaderLoader;
 class SystemClipboard;
 class RawSystemClipboard;
@@ -97,8 +97,17 @@ class ClipboardWriter : public GarbageCollected<ClipboardWriter>,
       DOMArrayBuffer* raw_data,
       scoped_refptr<base::SingleThreadTaskRunner> task_runner) = 0;
 
-  SystemClipboard* system_clipboard() { return system_clipboard_; }
-  RawSystemClipboard* raw_system_clipboard() { return raw_system_clipboard_; }
+  // SystemClipboard and RawSystemClipboard are bound to LocalFrame, so the
+  // bound LocalFrame must still be valid by the time they're used.
+  SystemClipboard* system_clipboard() {
+    DCHECK(promise_->GetLocalFrame());
+    return system_clipboard_;
+  }
+
+  RawSystemClipboard* raw_system_clipboard() {
+    DCHECK(promise_->GetLocalFrame());
+    return raw_system_clipboard_;
+  }
 
   // This ClipboardPromise owns this ClipboardWriter. Subclasses use `promise_`
   // to report success or failure, or to obtain the execution context.