Use platform agnostic web path implementation

This implementation is nearly identical to a UnixPath class I wrote a couple
years ago:

- https://github.com/GoogleCloudPlatform/google-cloud-java/blob/01812a30f31151db6678280ab4969c5337f49d7a/google-cloud-contrib/google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/UnixPath.java
- https://github.com/GoogleCloudPlatform/google-cloud-java/blob/01812a30f31151db6678280ab4969c5337f49d7a/google-cloud-contrib/google-cloud-nio/src/test/java/com/google/cloud/storage/contrib/nio/UnixPathTest.java

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=146824229

java/io/bazel/rules/closure/BUILD

@@ -42,6 +42,16 @@ java_library(
     deps = ["@com_google_guava"],
 )
 
+java_library(
+    name = "webpath",
+    srcs = ["Webpath.java"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "@com_google_code_findbugs_jsr305",
+        "@com_google_guava",
+    ],
+)
+
 java_proto_library(
     name = "build_info_java_proto",
     src = "build_info.proto",