Zero-initialize uniform data in SkRuntimeEffectBuilder

Change-Id: Id7445c28fca3a74cb2716832e821d651be7bb883
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/473142
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

include/core/SkData.h

@@ -86,6 +86,12 @@ public:
      */
     static sk_sp<SkData> MakeUninitialized(size_t length);
 
+    /**
+     *  Create a new data with zero-initialized contents. The caller should call writable_data()
+     *  to write into the buffer, but this must be done before another ref() is made.
+     */
+    static sk_sp<SkData> MakeZeroInitialized(size_t length);
+
     /**
      *  Create a new dataref by copying the specified c-string
      *  (a null-terminated array of bytes). The returned SkData will have size()

include/effects/SkRuntimeEffect.h

@@ -380,7 +380,7 @@ protected:
     SkRuntimeEffectBuilder() = delete;
     explicit SkRuntimeEffectBuilder(sk_sp<SkRuntimeEffect> effect)
             : fEffect(std::move(effect))
-            , fUniforms(SkData::MakeUninitialized(fEffect->uniformSize()))
+            , fUniforms(SkData::MakeZeroInitialized(fEffect->uniformSize()))
             , fChildren(fEffect->children().size()) {}
 
     SkRuntimeEffectBuilder(SkRuntimeEffectBuilder&&) = default;

src/core/SkData.cpp

@@ -111,6 +111,14 @@ sk_sp<SkData> SkData::MakeUninitialized(size_t length) {
     return PrivateNewWithCopy(nullptr, length);
 }
 
+sk_sp<SkData> SkData::MakeZeroInitialized(size_t length) {
+    auto data = MakeUninitialized(length);
+    if (length != 0) {
+        memset(data->writable_data(), 0, data->size());
+    }
+    return data;
+}
+
 sk_sp<SkData> SkData::MakeWithProc(const void* ptr, size_t length, ReleaseProc proc, void* ctx) {
     return sk_sp<SkData>(new SkData(ptr, length, proc, ctx));
 }