Add assertHeld() to SkMutex.

src/pdf/SkPDFGraphicState.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPDFFormXObject.h"
 #include "SkPDFGraphicState.h"
 #include "SkPDFUtils.h"
@@ skipping 96 matching lines @@
         return CanonicalPaints()[index].fGraphicState;
     }
     GSCanonicalEntry newEntry(new SkPDFGraphicState(paint));
     CanonicalPaints().push(newEntry);
     return newEntry.fGraphicState;
 }
 
 // static
 SkPDFObject* SkPDFGraphicState::GetInvertFunction() {
     // This assumes that canonicalPaintsMutex is held.
+    CanonicalPaintsMutex().assertHeld();
     static SkPDFStream* invertFunction = NULL;
     if (!invertFunction) {
         // Acrobat crashes if we use a type 0 function, kpdf crashes if we use
         // a type 2 function, so we use a type 4 function.
         SkAutoTUnref<SkPDFArray> domainAndRange(new SkPDFArray);
         domainAndRange->reserve(2);
         domainAndRange->appendInt(0);
         domainAndRange->appendInt(1);
 
         static const char psInvert[] = "{1 exch sub}";
@@ skipping 152 matching lines @@
     }
     if (bXfermodeName < 0 || bXfermodeName > SkXfermode::kLastMode ||
             blend_mode_from_xfermode(bXfermodeName) == NULL) {
         bXfermodeName = SkXfermode::kSrcOver_Mode;
     }
     const char* bXfermodeString = blend_mode_from_xfermode(bXfermodeName);
     SkASSERT(bXfermodeString != NULL);
 
     return strcmp(aXfermodeString, bXfermodeString) == 0;
 }