Fix a small error in exception handling in convertToBlob

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

Index: third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
diff --git a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
index 550ae97f7812703f3bfd86bc1fb93d68371313ce..d04a4cd040075225594278e464eb9b30780d408e 100644
--- a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
+++ b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
@@ -203,6 +203,12 @@ ScriptPromise OffscreenCanvas::convertToBlob(ScriptState* scriptState,
     return exceptionState.reject(scriptState);
   }
 
+  if (!width() || !height()) {
+    exceptionState.throwDOMException(
+        IndexSizeError, "Zero-sized OffscreenCanvas cannot be transferred.");

[xlai (Olivia), 2016/11/21 16:34:00]

Also, change the error msg. I think it has nothing to do with "transfer".

[xidachen, 2016/11/21 16:40:28]

Done.

+    return exceptionState.reject(scriptState);
+  }
+
   if (!this->isPaintable()) {
     return ScriptPromise();

[xlai (Olivia), 2016/11/21 16:34:00]

Actually, the third case is already handled in this if block
(!this->isPaintable()) but it's just returning an empty promise. Try to throw an
exception here instead of creating a new if block.

[xidachen, 2016/11/21 16:40:28]

Done, makes perfect sense.

   }