Closure: fall back to system `java` binary if jdk not on platform

R=agrieve@chromium.org

Fixed: 1038963
Change-Id: I0101e1ab7e2fe0159465d134c39971331d8b2340
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1985034
Commit-Queue: Dan Beam <dbeam@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Dan Beam <dbeam@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728317}

third_party/closure_compiler/compile_js.gni

@@ -60,6 +60,9 @@ template("js_library") {
                              "testonly",
                              "visibility",
                            ])
+    inputs = [
+      "$script_path/compiler.py",
+    ]
     output_file = "$target_gen_dir/$target_name.js_library"
     outputs = [
       output_file,

third_party/closure_compiler/compiler.py

@@ -17,6 +17,9 @@ import processor
 
 
 _CURRENT_DIR = os.path.join(os.path.dirname(__file__))
+_JAVA_BIN = "java"
+_JDK_PATH = os.path.join(_CURRENT_DIR, "..", "jdk", "current", "bin", _JAVA_BIN)
+_JAVA_PATH = _JDK_PATH if os.path.isfile(_JDK_PATH) else _JAVA_BIN
 
 
 class Compiler(object):
@@ -24,11 +27,11 @@ class Compiler(object):
   and produce minified output."""
 
   _JAR_COMMAND = [
-    os.path.join(_CURRENT_DIR, "..", "jdk", "current", "bin", "java"),
-    "-jar",
-    "-Xms1024m",
-    "-client",
-    "-XX:+TieredCompilation"
+      _JAVA_PATH,
+      "-jar",
+      "-Xms1024m",
+      "-client",
+      "-XX:+TieredCompilation",
   ]
 
   _POLYMER_EXTERNS = os.path.join(_CURRENT_DIR, "externs", "polymer-1.0.js")