Fix crashes when FileWriter methods are called after context is destroyed.

third_party/WebKit/Source/modules/filesystem/FileWriter.cpp

 /*
  * Copyright (C) 2010 Google Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 68 matching lines @@
   }
   resetWriter();
 }
 
 bool FileWriter::hasPendingActivity() const {
   return m_operationInProgress != OperationNone ||
          m_queuedOperation != OperationNone || m_readyState == kWriting;
 }
 
 void FileWriter::write(Blob* data, ExceptionState& exceptionState) {
+  if (!getExecutionContext())
+    return;
   ASSERT(data);
   ASSERT(writer());
   ASSERT(m_truncateLength == -1);
   if (m_readyState == kWriting) {
     setError(FileError::kInvalidStateErr, exceptionState);
     return;
   }
   if (m_recursionDepth > kMaxRecursionDepth) {
     setError(FileError::kSecurityErr, exceptionState);
     return;
   }
 
   m_blobBeingWritten = data;
   m_readyState = kWriting;
   m_bytesWritten = 0;
   m_bytesToWrite = data->size();
   ASSERT(m_queuedOperation == OperationNone);
   if (m_operationInProgress != OperationNone) {
     // We must be waiting for an abort to complete, since m_readyState wasn't
     // kWriting.
     ASSERT(m_operationInProgress == OperationAbort);
     m_queuedOperation = OperationWrite;
   } else
     doOperation(OperationWrite);
 
   fireEvent(EventTypeNames::writestart);
 }
 
 void FileWriter::seek(long long position, ExceptionState& exceptionState) {
+  if (!getExecutionContext())
+    return;
   ASSERT(writer());
   if (m_readyState == kWriting) {
     setError(FileError::kInvalidStateErr, exceptionState);
     return;
   }
 
   ASSERT(m_truncateLength == -1);
   ASSERT(m_queuedOperation == OperationNone);
   seekInternal(position);
 }
 
 void FileWriter::truncate(long long position, ExceptionState& exceptionState) {
+  if (!getExecutionContext())
+    return;
   ASSERT(writer());
   ASSERT(m_truncateLength == -1);
   if (m_readyState == kWriting || position < 0) {
     setError(FileError::kInvalidStateErr, exceptionState);
     return;
   }
   if (m_recursionDepth > kMaxRecursionDepth) {
     setError(FileError::kSecurityErr, exceptionState);
     return;
   }
 
   m_readyState = kWriting;
   m_bytesWritten = 0;
   m_bytesToWrite = 0;
   m_truncateLength = position;
   ASSERT(m_queuedOperation == OperationNone);
   if (m_operationInProgress != OperationNone) {
     // We must be waiting for an abort to complete, since m_readyState wasn't
     // kWriting.
     ASSERT(m_operationInProgress == OperationAbort);
     m_queuedOperation = OperationTruncate;
   } else
     doOperation(OperationTruncate);
   fireEvent(EventTypeNames::writestart);
 }
 
 void FileWriter::abort(ExceptionState& exceptionState) {
+  if (!getExecutionContext())
+    return;
   ASSERT(writer());
   if (m_readyState != kWriting)
     return;
   ++m_numAborts;
 
   doOperation(OperationAbort);
   signalCompletion(FileError::kAbortErr);
 }
 
 void FileWriter::didWrite(long long bytes, bool complete) {
@@ skipping 145 matching lines @@
 
 DEFINE_TRACE(FileWriter) {
   visitor->trace(m_error);
   visitor->trace(m_blobBeingWritten);
   EventTargetWithInlineData::trace(visitor);
   FileWriterBase::trace(visitor);
   SuspendableObject::trace(visitor);
 }
 
 }  // namespace blink