Make attrib missing buffer message clearer.

Source/core/html/canvas/WebGLRenderingContext.cpp

Index: Source/core/html/canvas/WebGLRenderingContext.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContext.cpp b/Source/core/html/canvas/WebGLRenderingContext.cpp
index 447cbb56c1076a1e00f5f3523516a84088e46dd1..20fa595b39da22a5e0ff80a590017e3dd1b03291 100644
--- a/Source/core/html/canvas/WebGLRenderingContext.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContext.cpp
@@ -1793,17 +1793,21 @@ void WebGLRenderingContext::disableVertexAttribArray(GLuint index)
     m_context->disableVertexAttribArray(index);
 }
 
-bool WebGLRenderingContext::validateRenderingState()
+bool WebGLRenderingContext::validateRenderingState(const char* functionName)
 {
-    if (!m_currentProgram)
+    if (!m_currentProgram) {
+        synthesizeGLError(GL_INVALID_OPERATION, functionName, "no valid shader program in use");
         return false;
+    }
 
     // Look in each enabled vertex attrib and check if they've been bound to a buffer.
     for (unsigned i = 0; i < m_onePlusMaxEnabledAttribIndex; ++i) {
         const WebGLVertexArrayObjectOES::VertexAttribState& state = m_boundVertexArrayObject->getVertexAttribState(i);
         if (state.enabled
-            && (!state.bufferBinding || !state.bufferBinding->object()))
+            && (!state.bufferBinding || !state.bufferBinding->object())) {
+            synthesizeGLError(GL_INVALID_OPERATION, functionName, String::format("attribute %d is enabled but has no buffer bound", i).utf8().data());
             return false;
+        }
     }
 
     return true;
@@ -5219,8 +5223,7 @@ bool WebGLRenderingContext::validateDrawArrays(const char* functionName, GLenum
         return false;
     }
 
-    if (!validateRenderingState()) {
-        synthesizeGLError(GL_INVALID_OPERATION, functionName, "attribs not setup correctly");
+    if (!validateRenderingState(functionName)) {
         return false;
     }
 
@@ -5270,8 +5273,7 @@ bool WebGLRenderingContext::validateDrawElements(const char* functionName, GLenu
         return false;
     }
 
-    if (!validateRenderingState()) {
-        synthesizeGLError(GL_INVALID_OPERATION, functionName, "attribs not setup correctly");
+    if (!validateRenderingState(functionName)) {
         return false;
     }