Reland 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 24c682a94055acccd1316f920e578e5df4775386..3f038c276abdaa800e33b509a2acaadf6bb1604e 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"
@@ -21,14 +22,38 @@ public:
     static CanvasAsyncBlobCreator* create(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,
+        IdleTaskNotSupported // Idle tasks are not implemented for some image types
+    };
+    // Methods are virtual for mocking in unit tests
+    virtual void signalTaskSwitchInStartTimeoutEventForTesting() { }
+    virtual void signalTaskSwitchInCompleteTimeoutEventForTesting() { }
 
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         visitor->trace(m_data);
     }
 
-private:
+protected:
     CanvasAsyncBlobCreator(DOMUint8ClampedArray* data, const String& mimeType, const IntSize&, BlobCallback*);
+    // Methods are virtual for unit testing
+    virtual void scheduleInitiatePngEncoding();
+    virtual void idleEncodeRowsPng(double deadlineSeconds);
+    virtual void postDelayedTaskToMainThread(const WebTraceLocation&, SameThreadTask*, double delayMs);
+    virtual void signalAlternativeCodePathFinishedForTesting() { }
+    virtual void createBlobAndInvokeCallback();
+    virtual void createNullAndInvokeCallback();
+
+    void initiatePngEncoding(double deadlineSeconds);
+    IdleTaskStatus m_idleTaskStatus;
+
+private:
+    friend class CanvasAsyncBlobCreatorTest;
 
     OwnPtr<PNGImageEncoderState> m_pngEncoderState;
     OwnPtr<JPEGImageEncoderState> m_jpegEncoderState;
@@ -41,15 +66,16 @@ private:
     const String m_mimeType;
     CrossThreadPersistent<BlobCallback> m_callback;
 
-    void initiatePngEncoding(double deadlineSeconds);
     void scheduleIdleEncodeRowsPng();
-    void idleEncodeRowsPng(double deadlineSeconds);
 
-    void initiateJpegEncoding(const double& quality);
+    bool initializePngStruct();
+    void encodeRowsPngOnMainThread(); // Similar to idleEncodeRowsPng without deadline
+    void encodeImageOnEncoderThread(double quality);
 
-    void createBlobAndCall();
+    void initiateJpegEncoding(const double& quality);
 
-    void encodeImageOnEncoderThread(double quality);
+    void idleTaskStartTimeoutEvent(double quality);
+    void idleTaskCompleteTimeoutEvent();
 };
 
 } // namespace blink