Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/EXTDrawBuffers.cpp

Index: Source/core/html/canvas/EXTDrawBuffers.cpp
diff --git a/Source/core/html/canvas/EXTDrawBuffers.cpp b/Source/core/html/canvas/EXTDrawBuffers.cpp
index ebee69d959ea8ef35f76cf657559c9248b1bbcae..6b00b843b54b3c2040941c5da57d1e688c6fa1fe 100644
--- a/Source/core/html/canvas/EXTDrawBuffers.cpp
+++ b/Source/core/html/canvas/EXTDrawBuffers.cpp
@@ -35,13 +35,18 @@ EXTDrawBuffers::EXTDrawBuffers(WebGLRenderingContext* context)
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);
-    context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_EXT_draw_buffers");
+    enable();
 }
 
 EXTDrawBuffers::~EXTDrawBuffers()
 {
 }
 
+void EXTDrawBuffers::enable()
+{
+    m_context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_EXT_draw_buffers");
+}
+
 WebGLExtension::ExtensionName EXTDrawBuffers::getName() const
 {
     return WebGLExtension::EXTDrawBuffersName;
@@ -67,7 +72,7 @@ const char* EXTDrawBuffers::getExtensionName()
 
 void EXTDrawBuffers::drawBuffersEXT(const Vector<GC3Denum>& buffers)
 {
-    if (m_context->isContextLost())
+    if (isLost())
         return;
     GC3Dsizei n = buffers.size();
     const GC3Denum* bufs = buffers.data();