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

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

Index: third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp
diff --git a/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp b/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp
index e8d9ee846d1ac3f0b0e95e7e5915a68a22b34ce5..3ffa394c3110a1ba86bb439b89749ac374d53bc9 100644
--- a/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp
+++ b/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp
@@ -2211,8 +2211,13 @@ String WebGL2RenderingContextBase::getActiveUniformBlockName(WebGLProgram* progr
         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);
 }