Load/Save ShaderVariableBuffer::memberIndexes in one memcpy

ShaderVariableBuffer::memberIndexes is std::vector<unsigned int>, and
can be quite huge (164 on some programs in blade_and_soul_revolution).
Right now it is calling readInt for individual index and then push_back.
This causes vector to be copied as it grows size. This CL makes one
memcpy for entire vector and increase size only once.

Bug: b/275102061
Change-Id: I983ad289b126dbfd430cf94a3772c2bfd93cb1c6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4775835
Reviewed-by: Roman Lavrov <romanl@google.com>
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>

src/libANGLE/Program.cpp

@@ -451,9 +451,10 @@ void WriteShaderVariableBuffer(BinaryOutputStream *stream, const ShaderVariableB
     stream->writeInt(var.dataSize);
 
     stream->writeInt(var.memberIndexes.size());
-    for (unsigned int memberCounterIndex : var.memberIndexes)
+    if (!var.memberIndexes.empty())
     {
-        stream->writeInt(memberCounterIndex);
+        stream->writeBytes(reinterpret_cast<const unsigned char *>(var.memberIndexes.data()),
+                           sizeof(*var.memberIndexes.data()) * var.memberIndexes.size());
     }
 }
 
@@ -464,10 +465,13 @@ void LoadShaderVariableBuffer(BinaryInputStream *stream, ShaderVariableBuffer *v
     var->binding  = stream->readInt<int>();
     var->dataSize = stream->readInt<unsigned int>();
 
+    ASSERT(var->memberIndexes.empty());
     size_t numMembers = stream->readInt<size_t>();
-    for (size_t blockMemberIndex = 0; blockMemberIndex < numMembers; blockMemberIndex++)
+    if (numMembers > 0)
     {
-        var->memberIndexes.push_back(stream->readInt<unsigned int>());
+        var->memberIndexes.resize(numMembers);
+        stream->readBytes(reinterpret_cast<unsigned char *>(var->memberIndexes.data()),
+                          sizeof(unsigned int) * var->memberIndexes.size());
     }
 }