Add a flag to ANGLE to force immediate swap.

src/libGLESv2/renderer/SwapChain.h

@@ -12,6 +12,10 @@
 
 #include "common/angleutils.h"
 
+#if !defined(ANGLE_FORCE_VSYNC_OFF)
+#define ANGLE_FORCE_VSYNC_OFF 0
+#endif
+
 namespace rx
 {
 

src/libGLESv2/renderer/SwapChain11.cpp

@@ -670,7 +670,12 @@ EGLint SwapChain11::swapRect(EGLint x, EGLint y, EGLint width, EGLint height)
 
     // Draw
     deviceContext->Draw(4, 0);
+
+#if ANGLE_FORCE_VSYNC_OFF
+    result = mSwapChain->Present(0, 0);
+#else
     result = mSwapChain->Present(mSwapInterval, 0);
+#endif
 
     if (result == DXGI_ERROR_DEVICE_REMOVED)
     {

src/libGLESv2/renderer/SwapChain9.cpp

@@ -71,6 +71,9 @@ void SwapChain9::release()
 
 static DWORD convertInterval(EGLint interval)
 {
+#if ANGLE_FORCE_VSYNC_OFF
+    return D3DPRESENT_INTERVAL_IMMEDIATE;
+#else
     switch(interval)
     {
       case 0: return D3DPRESENT_INTERVAL_IMMEDIATE;
@@ -82,6 +85,7 @@ static DWORD convertInterval(EGLint interval)
     }
 
     return D3DPRESENT_INTERVAL_DEFAULT;
+#endif
 }
 
 EGLint SwapChain9::resize(int backbufferWidth, int backbufferHeight)