add gm that exercises compose shader allocations

src/core/SkSmallAllocator.h

 /*
  * Copyright 2014 Google, Inc
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSmallAllocator_DEFINED
 #define SkSmallAllocator_DEFINED
 
@@ skipping 62 matching lines @@
      */
     template<typename T> void* reserveT(size_t storageRequired = sizeof(T)) {
         SkASSERT(fNumObjects < kMaxObjects);
         SkASSERT(storageRequired >= sizeof(T));
         if (kMaxObjects == fNumObjects) {
             return nullptr;
         }
         const size_t storageRemaining = sizeof(fStorage) - fStorageUsed;
         Rec* rec = &fRecs[fNumObjects];
         if (storageRequired > storageRemaining) {
-            // Allocate on the heap. Ideally we want to avoid this situation,
-            // but we're not sure we can catch all callers, so handle it but
-            // assert false in debug mode.
-            SkASSERT(false);
+            // Allocate on the heap. Ideally we want to avoid this situation.
+
+            // With the gm composeshader_bitmap2, storage required is 4476
+            // and storage remaining is 3392. Increasing the base storage
+            // causes google 3 tests to fail.
+
             rec->fStorageSize = 0;
             rec->fHeapStorage = sk_malloc_throw(storageRequired);
             rec->fObj = static_cast<void*>(rec->fHeapStorage);
         } else {
             // There is space in fStorage.
             rec->fStorageSize = storageRequired;
             rec->fHeapStorage = nullptr;
             rec->fObj = static_cast<void*>(fStorage.fBytes + fStorageUsed);
             fStorageUsed += storageRequired;
         }
@@ skipping 37 matching lines @@
     };
 
     Storage     fStorage;
     // Number of bytes used so far.
     size_t      fStorageUsed;
     uint32_t    fNumObjects;
     Rec         fRecs[kMaxObjects];
 };
 
 #endif // SkSmallAllocator_DEFINED