Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/WebGLCompressedTextureATC.cpp

Index: Source/core/html/canvas/WebGLCompressedTextureATC.cpp
diff --git a/Source/core/html/canvas/WebGLCompressedTextureATC.cpp b/Source/core/html/canvas/WebGLCompressedTextureATC.cpp
index db998a9195b23c7dc8cb2680235ab6f893719850..1593ab356b7aac1462786215846c5d28130de3fd 100644
--- a/Source/core/html/canvas/WebGLCompressedTextureATC.cpp
+++ b/Source/core/html/canvas/WebGLCompressedTextureATC.cpp
@@ -35,15 +35,20 @@ WebGLCompressedTextureATC::WebGLCompressedTextureATC(WebGLRenderingContext* cont
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);
-    context->addCompressedTextureFormat(Extensions3D::COMPRESSED_ATC_RGB_AMD);
-    context->addCompressedTextureFormat(Extensions3D::COMPRESSED_ATC_RGBA_EXPLICIT_ALPHA_AMD);
-    context->addCompressedTextureFormat(Extensions3D::COMPRESSED_ATC_RGBA_INTERPOLATED_ALPHA_AMD);
+    enable();
 }
 
 WebGLCompressedTextureATC::~WebGLCompressedTextureATC()
 {
 }
 
+void WebGLCompressedTextureATC::enable()
+{
+    m_context->addCompressedTextureFormat(Extensions3D::COMPRESSED_ATC_RGB_AMD);
+    m_context->addCompressedTextureFormat(Extensions3D::COMPRESSED_ATC_RGBA_EXPLICIT_ALPHA_AMD);
+    m_context->addCompressedTextureFormat(Extensions3D::COMPRESSED_ATC_RGBA_INTERPOLATED_ALPHA_AMD);
+}
+
 WebGLExtension::ExtensionName WebGLCompressedTextureATC::getName() const
 {
     return WebGLCompressedTextureATCName;