toBlob: If idle image encoding is postponed for too long, switch to main thread

third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h

Index: third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
diff --git a/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h b/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
index 391a9ce9a387789b3fe74163480054a777b39a63..0ac104d548994a9c6976cdaa0af541dc7d2ad08a 100644
--- a/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
+++ b/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
@@ -5,6 +5,7 @@
 #include "core/CoreExport.h"
 #include "core/dom/DOMTypedArray.h"
 #include "core/fileapi/BlobCallback.h"
+#include "platform/Task.h"
 #include "platform/geometry/IntSize.h"
 #include "platform/heap/Handle.h"
 #include "wtf/OwnPtr.h"
@@ -23,11 +24,32 @@ public:
     static PassRefPtr<CanvasAsyncBlobCreator> create(PassRefPtr<DOMUint8ClampedArray> unpremultipliedRGBAImageData, const String& mimeType, const IntSize&, BlobCallback*);
     void scheduleAsyncBlobCreation(bool canUseIdlePeriodScheduling, double quality = 0.0);
     virtual ~CanvasAsyncBlobCreator();
+    enum IdleTaskStatus {
+        IdleTaskNotStarted,
+        IdleTaskStarted,
+        IdleTaskCompleted,
+        IdleTaskFailed,
+        IdleTaskSwitchedToMainThreadTask,
+        Default // Idle tasks are not implemented for some image types
+    };
+    virtual void signalTaskSwitchInStartTimeoutEventForTesting() { }
+    virtual void signalTaskSwitchInCompleteTimeoutEventForTesting() { }
 
-private:
+protected:
     CanvasAsyncBlobCreator(PassRefPtr<DOMUint8ClampedArray> data, const String& mimeType, const IntSize&, BlobCallback*);
-    void scheduleCreateBlobAndCallOnMainThread();
-    void scheduleCreateNullptrAndCallOnMainThread();
+    virtual void scheduleInitiatePngEncoding();
+    virtual void idleEncodeRowsPng(double deadlineSeconds);
+    virtual void postDelayedTaskToMainThread(const WebTraceLocation&, Task*, double delayMs);
+    virtual void clearAlternativeSelfReference();
+    virtual void createBlobAndCall();
+    virtual void createNullptrAndCall();
+
+    void clearSelfReference();
+    void initiatePngEncoding(double deadlineSeconds);
+    IdleTaskStatus m_idleTaskStatus;
+
+private:
+    friend class CanvasAsyncBlobCreatorTest;
 
     OwnPtr<PNGImageEncoderState> m_pngEncoderState;
     OwnPtr<JPEGImageEncoderState> m_jpegEncoderState;
@@ -40,18 +62,22 @@ private:
     const String m_mimeType;
     CrossThreadPersistent<BlobCallback> m_callback;
 
+    // To keep this asyncBlobCreator alive before async encoding task completes
+    // Used by all image types
     RefPtr<CanvasAsyncBlobCreator> m_selfRef;
-    void clearSelfReference();
+    // To keep this asyncBlobCreator alive before the alternative code path (for
+    // the case when idle task is postponed for too long) is confirmed not to
+    // continue any more; Used by png image type only
+    RefPtr<CanvasAsyncBlobCreator> m_alternativeSelfRef;
 
-    void initiatePngEncoding(double deadlineSeconds);
-    void scheduleIdleEncodeRowsPng();
-    void idleEncodeRowsPng(double deadlineSeconds);
+    bool initializePngStruct();
+    void encodeRowsPngOnMainThread(); // Similar to idleEncodeRowsPng without deadline
+    void encodeImageOnEncoderThread(double quality);
 
     void initiateJpegEncoding(const double& quality);
 
-    void createBlobAndCall();
-
-    void encodeImageOnEncoderThread(double quality);
+    void idleTaskStartTimeoutEvent(double quality);
+    void idleTaskCompleteTimeoutEvent();
 };
 
 } // namespace blink