Revert of Fixes for SkRWBuffer

src/core/SkRWBuffer.cpp

Index: src/core/SkRWBuffer.cpp
diff --git a/src/core/SkRWBuffer.cpp b/src/core/SkRWBuffer.cpp
index bbf88ddfe304abccff809db917bda89715705c25..f0b565edf3f685360844dace2af2997de810b5ed 100644
--- a/src/core/SkRWBuffer.cpp
+++ b/src/core/SkRWBuffer.cpp
@@ -42,8 +42,6 @@
         return amount;
     }
 
-    // Do not call in the reader thread, since the writer may be updating fUsed.
-    // (The assertion is still true, but TSAN still may complain about its raciness.)
     void validate() const {
 #ifdef SK_DEBUG
         SkASSERT(fCapacity > 0);
@@ -96,7 +94,7 @@
         }
     }
 
-    void validate(size_t minUsed, const SkBufferBlock* tail = nullptr) const {
+    void validate(size_t minUsed, SkBufferBlock* tail = nullptr) const {
 #ifdef SK_DEBUG
         SkASSERT(fRefCnt > 0);
         size_t totalUsed = 0;
@@ -134,6 +132,7 @@
 
 SkROBuffer::~SkROBuffer() {
     if (fHead) {
+        fHead->validate(fAvailable);
         fHead->unref();
     }
 }
@@ -143,7 +142,7 @@
 }
 
 void SkROBuffer::Iter::reset(const SkROBuffer* buffer) {
-    if (buffer && buffer->fHead) {
+    if (buffer) {
         fBlock = &buffer->fHead->fBlock;
         fRemaining = buffer->fAvailable;
     } else {