Fix the crash problem on WebGL2 conformance test of negative state api.

third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "modules/webgl/WebGL2RenderingContextBase.h"
 
 #include "bindings/modules/v8/WebGLAny.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/HTMLImageElement.h"
@@ skipping 2193 matching lines @@
         return String();
 
     GLint maxNameLength = -1;
     webContext()->getProgramiv(objectOrZero(program), GL_ACTIVE_UNIFORM_BLOCK_MAX_NAME_LENGTH, &maxNameLength);
     if (maxNameLength <= 0) {
         // This state indicates that there are no active uniform blocks
         synthesizeGLError(GL_INVALID_VALUE, "getActiveUniformBlockName", "invalid uniform block index");
         return String();
     }
     OwnPtr<GLchar[]> name = adoptArrayPtr(new GLchar[maxNameLength]);
-    GLsizei length;
+
+    GLsizei length = -1;

[Zhenyao Mo, 2015/12/02 00:46:10]

Initialize length to 0 is enough, returning String(name.get(), 0) is the same as
returning String(), I think.

     webContext()->getActiveUniformBlockName(objectOrZero(program), uniformBlockIndex, maxNameLength, &length, name.get());
+    if (length <= 0) {
+        synthesizeGLError(GL_INVALID_VALUE, "getActiveUniformBlockName", "invalid uniform block name string");

[Ken Russell (switch to Gerrit), 2015/12/02 00:38:42]

Is it necessary to synthesize a GL error? One should already have been
generated. See
https://www.opengl.org/sdk/docs/man3/xhtml/glGetActiveUniformBlockName.xml . "If
an error occurs, nothing will be written to uniformBlockName or length." In this
case perhaps the check should be "if (length < 0)".

+        return String();
+    }
     return String(name.get(), length);
 }
 
 void WebGL2RenderingContextBase::uniformBlockBinding(WebGLProgram* program, GLuint uniformBlockIndex, GLuint uniformBlockBinding)
 {
     if (isContextLost() || !validateWebGLObject("uniformBlockBinding", program))
         return;
 
     webContext()->uniformBlockBinding(objectOrZero(program), uniformBlockIndex, uniformBlockBinding);
 }
@@ skipping 899 matching lines @@
 GLenum WebGL2RenderingContextBase::boundFramebufferColorFormat()
 {
     if (m_readFramebufferBinding && m_readFramebufferBinding->object())
         return m_readFramebufferBinding->colorBufferFormat();
     if (m_requestedAttributes.alpha())
         return GL_RGBA;
     return GL_RGB;
 }
 
 } // namespace blink