In SkPDFDocument::emitPDF(), stop pre-calculating file offsets.

In SkPDFDocument::emitPDF(), stop pre-calculating file offsets.

* Add Streamer utility class which measures the current
  pdf offset by calling SkWStream::bytesWritten(). Calls
  SkPDFCatalog::setFileOffset() and SkPDFObject::emit() at
  the same time to guarantee that everything works out.

* SkPDFCatalog::setFileOffset() no longer calculates the
  object's size.

* SkPDFCatalog::setSubstituteResourcesOffsets() removed.

* SkPDFCatalog::emitSubstituteResources() removed and
  getSubstituteList() made public in its place.

* Remove SkPDFPage::getPageSize and SkPDFPage::emitPage.
  Replace with SkPDFPage::getContentStream().

* SkPDFObject::getOutputSize no longer virtual, only used in
  unit tests.  All SkPDFObject subclasses getOutputSize()
  overrides removed.

* SkPDFObject::getIndirectOutputSize removed.

* PDFPrimitivesTest updated for new functions.

Review URL: https://codereview.chromium.org/846023003