Add validation for unsized BGRA texture formats.

BUG=angle:620

Change-Id: I956b7fc4ed0be99239e4ed1c63b51732727cc87f
Reviewed-on: https://chromium-review.googlesource.com/196840
Tested-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/Context.cpp b/src/libGLESv2/Context.cpp
index 507af51..93ef49a 100644
--- a/src/libGLESv2/Context.cpp
+++ b/src/libGLESv2/Context.cpp
@@ -3879,6 +3879,13 @@
     if (mClientVersion == 3)
     {
         mExtensionStringList.push_back("GL_EXT_color_buffer_float");
+
+        mExtensionStringList.push_back("GL_EXT_read_format_bgra");
+
+        if (supportsBGRATextures())
+        {
+            mExtensionStringList.push_back("GL_EXT_texture_format_BGRA8888");
+        }
     }
 
     // Join the extension strings to one long string for use with GetString