Make WebGL extensions get lost when context is lost.

Source/core/html/canvas/OESTextureHalfFloat.cpp

Index: Source/core/html/canvas/OESTextureHalfFloat.cpp
diff --git a/Source/core/html/canvas/OESTextureHalfFloat.cpp b/Source/core/html/canvas/OESTextureHalfFloat.cpp
index 1d00ea8b038194c6fee9bfc8467d0477b466907c..1542bfcfab942ad9ccfef5af8b81e83a28171d8b 100644
--- a/Source/core/html/canvas/OESTextureHalfFloat.cpp
+++ b/Source/core/html/canvas/OESTextureHalfFloat.cpp
@@ -34,13 +34,17 @@ OESTextureHalfFloat::OESTextureHalfFloat(WebGLRenderingContext* context)
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);

[Ken Russell (switch to Gerrit), 2013/06/05 00:46:38]

Missing call to enable()?

-    context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_OES_texture_half_float");
 }
 
 OESTextureHalfFloat::~OESTextureHalfFloat()
 {
 }
 
+void OESTextureHalfFloat::enable()
+{
+    m_context->graphicsContext3D()->getExtensions()->ensureEnabled("GL_OES_texture_half_float");
+}
+
 WebGLExtension::ExtensionName OESTextureHalfFloat::getName() const
 {
     return OESTextureHalfFloatName;