skip unneeded header from writeFlattenable when building font-cache-key. Saves ~30% in size

src/core/SkPaint.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPaint.h"
 #include "SkAutoKern.h"
 #include "SkChecksum.h"
@@ skipping 1549 matching lines @@
         rec->ignoreGamma();
     }
     if (!boostContrast) {
         rec->setContrast(0);
     }
 
     int entryCount = 1;
     size_t descSize = sizeof(*rec);
 
     if (pe) {
-        peBuffer->writeFlattenable(pe);
+        pe->flatten(*peBuffer);
         descSize += peBuffer->bytesWritten();
         entryCount += 1;
         rec->fMaskFormat = SkMask::kA8_Format;  // force antialiasing when we do the scan conversion
         // seems like we could support kLCD as well at this point...
     }
     if (mf) {
-        mfBuffer->writeFlattenable(mf);
+        mf->flatten(*mfBuffer);
         descSize += mfBuffer->bytesWritten();
         entryCount += 1;
         rec->fMaskFormat = SkMask::kA8_Format;   // force antialiasing with maskfilters
         /* Pre-blend is not currently applied to filtered text.
            The primary filter is blur, for which contrast makes no sense,
            and for which the destination guess error is more visible.
            Also, all existing users of blur have calibrated for linear. */
         rec->ignorePreBlend();
     }
     if (ra) {
-        raBuffer->writeFlattenable(ra);
+        ra->flatten(*raBuffer);
         descSize += raBuffer->bytesWritten();
         entryCount += 1;
         rec->fMaskFormat = SkMask::kA8_Format;  // force antialiasing when we do the scan conversion
     }
 
     ///////////////////////////////////////////////////////////////////////////
     // Now that we're done tweaking the rec, call the PostMakeRec cleanup
     SkScalerContext::PostMakeRec(paint, rec);
 
     descSize += SkDescriptor::ComputeOverhead(entryCount);
@@ skipping 772 matching lines @@
 }
 
 uint32_t SkPaint::getHash() const {
     // We're going to hash 10 pointers and 7 32-bit values, finishing up with fBitfields,
     // so fBitfields should be 10 pointers and 6 32-bit values from the start.
     static_assert(offsetof(SkPaint, fBitfields) == 9 * sizeof(void*) + 6 * sizeof(uint32_t),
                   "SkPaint_notPackedTightly");
     return SkChecksum::Murmur3(reinterpret_cast<const uint32_t*>(this),
                                offsetof(SkPaint, fBitfields) + sizeof(fBitfields));
 }