Add trace event when GrBufferAllocPool unmaps a buffer indicating what % of the buffer was unwritte…

src/gpu/GrBufferAllocPool.h

Index: src/gpu/GrBufferAllocPool.h
diff --git a/src/gpu/GrBufferAllocPool.h b/src/gpu/GrBufferAllocPool.h
index 291d781ac6c00878eded1d00569f1c1b34884498..e3d398204bd5a443973162ea25c194aecb787930 100644
--- a/src/gpu/GrBufferAllocPool.h
+++ b/src/gpu/GrBufferAllocPool.h
@@ -155,7 +155,7 @@ private:
 
     bool createBlock(size_t requestSize);
     void destroyBlock();
-    void flushCpuData(GrGeometryBuffer* buffer, size_t flushSize);
+    void flushCpuData(const BufferBlock& block, size_t flushSize);
 #ifdef SK_DEBUG
     void validate(bool unusedBlockAllowed = false) const;
 #endif