Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/OESTextureFloatLinear.cpp

Index: Source/core/html/canvas/OESTextureFloatLinear.cpp
diff --git a/Source/core/html/canvas/OESTextureFloatLinear.cpp b/Source/core/html/canvas/OESTextureFloatLinear.cpp
index 04d59e22c240e8e585b393aa5411369665cecf78..a122b0a4e26983639dd64f06715e46ca9958b3dd 100644
--- a/Source/core/html/canvas/OESTextureFloatLinear.cpp
+++ b/Source/core/html/canvas/OESTextureFloatLinear.cpp
@@ -35,13 +35,18 @@ OESTextureFloatLinear::OESTextureFloatLinear(WebGLRenderingContext* context)
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);
-    context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_OES_texture_float_linear");
+    enable();
 }
 
 OESTextureFloatLinear::~OESTextureFloatLinear()
 {
 }
 
+void OESTextureFloatLinear::enable()
+{
+    m_context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_OES_texture_float_linear");
+}
+
 WebGLExtension::ExtensionName OESTextureFloatLinear::getName() const
 {
     return OESTextureFloatLinearName;