Split the RenderTarget classes based on if they are backing a SwapChain.

bug=angle:824

Change-Id: I89e475d4065102dbaa7fa1f1bfd02c7207def75c
Reviewed-on: https://chromium-review.googlesource.com/227600
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libGLESv2/renderer/RenderTarget.cpp b/src/libGLESv2/renderer/RenderTarget.cpp
index 75299ec..857fdc9 100644
--- a/src/libGLESv2/renderer/RenderTarget.cpp
+++ b/src/libGLESv2/renderer/RenderTarget.cpp
@@ -12,6 +12,15 @@
 {
 unsigned int RenderTarget::mCurrentSerial = 1;
 
+RenderTarget::RenderTarget()
+    : mSerial(issueSerials(1))
+{
+}
+
+RenderTarget::~RenderTarget()
+{
+}
+
 unsigned int RenderTarget::getSerial() const
 {
     return mSerial;
@@ -23,4 +32,5 @@
     mCurrentSerial += count;
     return firstSerial;
 }
-}
\ No newline at end of file
+
+}