[Resources] Only rewrite non-system resource IDs for webview

In monochrome webview mode onResourceLoaded currently rewrites all
resource ids inside resource arrays including system resource IDs. This
is a bug.

The first try to fix the bug (cl/952097) caused a performance regression
in webview startup so this is a different idea to fixing the same bug
that should hopefully not suffer from the same performance regression as
the previous.

Since resource IDs are sorted (so system resources are at the beginning
of the array).  This CL finds the index of the first non-system resource
ID and starts rewriting at that point.

NOTRY=true #win7_chromium_rel_ng extremely flakey

Bug: 821425
Change-Id: I9f6f3c517a8c09cbbefb9b584ab6f5bfc9c8477b
Reviewed-on: https://chromium-review.googlesource.com/999003
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549267}

build/android/gyp/util/resource_utils.py

@@ -244,6 +244,21 @@ def _CreateRJavaSourceFile(srcjar_dir, package, resources_by_type,
     f.write(java_file_contents)
 
 
+# Resource IDs inside resource arrays are sorted. Application resource IDs start
+# with 0x7f but system resource IDs start with 0x01 thus system resource ids are
+# always at the start of the array. This function finds the index of the first
+# non system resource id to be used for package ID rewriting (we should not
+# rewrite system resource ids).
+def _GetNonSystemIndex(entry):
+  """Get the index of the first application resource ID within a resource
+  array."""
+  res_ids = re.findall(r'0x[0-9a-f]{8}', entry.value)
+  for i, res_id in enumerate(res_ids):
+    if res_id.startswith('0x7f'):
+      return i
+  return len(res_ids)
+
+
 def _RenderRJavaSource(package, resources_by_type, rjava_build_options):
   """Render an R.java source file. See _CreateRJaveSourceFile for args info."""
   final_resources_by_type = collections.defaultdict(list)
@@ -262,6 +277,8 @@ def _RenderRJavaSource(package, resources_by_type, rjava_build_options):
   create_id = ('{{ e.resource_type }}.{{ e.name }} ^= packageIdTransform;')
   create_id_arr = ('{{ e.resource_type }}.{{ e.name }}[i] ^='
                    ' packageIdTransform;')
+  for_loop_condition  = ('int i = {{ startIndex(e) }}; i < '
+                         '{{ e.resource_type }}.{{ e.name }}.length; ++i')
 
   # Here we diverge from what aapt does. Because we have so many
   # resources, the onResourcesLoaded method was exceeding the 64KB limit that
@@ -292,7 +309,7 @@ public final class R {
         onResourcesLoaded{{ resource_type|title }}(packageIdTransform);
         {% for e in non_final_resources[resource_type] %}
         {% if e.java_type == 'int[]' %}
-        for(int i = 0; i < {{ e.resource_type }}.{{ e.name }}.length; ++i) {
+        for(""" + for_loop_condition + """) {
             """ + create_id_arr + """
         }
         {% endif %}
@@ -318,7 +335,8 @@ public final class R {
       resource_types=sorted(resources_by_type),
       has_on_resources_loaded=rjava_build_options.has_on_resources_loaded,
       final_resources=final_resources_by_type,
-      non_final_resources=non_final_resources_by_type)
+      non_final_resources=non_final_resources_by_type,
+      startIndex=_GetNonSystemIndex)
 
 
 def ExtractPackageFromManifest(manifest_path):