Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/OESTextureFloat.cpp

Index: Source/core/html/canvas/OESTextureFloat.cpp
diff --git a/Source/core/html/canvas/OESTextureFloat.cpp b/Source/core/html/canvas/OESTextureFloat.cpp
index d2f5a22ed2af7e6861584dde584d53a7e85e8627..729ff9b6e8b96069f5eae088dea18b721abf702f 100644
--- a/Source/core/html/canvas/OESTextureFloat.cpp
+++ b/Source/core/html/canvas/OESTextureFloat.cpp
@@ -34,13 +34,18 @@ OESTextureFloat::OESTextureFloat(WebGLRenderingContext* context)
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);
-    context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_OES_texture_float");
+    enable();
 }
 
 OESTextureFloat::~OESTextureFloat()
 {
 }
 
+void OESTextureFloat::enable()
+{
+    m_context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_OES_texture_float");
+}
+
 WebGLExtension::ExtensionName OESTextureFloat::getName() const
 {
     return OESTextureFloatName;