Add explicit UniqueID classes for GrGpuResource & GrSurfaceProxy

This sets the stage for using the Proxy's/RenderTargetContext's ID above the flush and the RenderTarget's/GrGpuResource's below the flush.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4650

Change-Id: I9f1e6b00c02a0691d90b58c49e1d8c60684884c1
Reviewed-on: https://skia-review.googlesource.com/4650
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/gl/GrGLRenderTarget.cpp b/src/gpu/gl/GrGLRenderTarget.cpp
index 5af5e67..45efba2 100644
--- a/src/gpu/gl/GrGLRenderTarget.cpp
+++ b/src/gpu/gl/GrGLRenderTarget.cpp
@@ -188,7 +188,7 @@
         // Due to this resource having both a texture and a renderbuffer component, dump as
         // skia/gpu_resources/resource_#/renderbuffer
         SkString dumpName("skia/gpu_resources/resource_");
-        dumpName.appendS32(this->uniqueID());
+        dumpName.appendU32(this->uniqueID().asUInt());
         dumpName.append("/renderbuffer");
 
         traceMemoryDump->dumpNumericValue(dumpName.c_str(), "size", "bytes", size);