[webui-cc] Default enable source maps on coverage builder

Early adopters of WebUI code coverage have quality checked the coverage
metrics and haven't found any issues. We feel confident source maps are
ready for general rollout.

To support load_time_data_deprecated.js being passed to build_webui this
CL pipes JS files through the create_js_source_maps step.

Change-Id: I6d923870d026d0aaa3f5b56882f609da59e7fb8e
Fixed: b/265971775
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4500455
Auto-Submit: Tibor Goldschwendt <tiborg@chromium.org>
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1139186}
diff --git a/docs/webui_build_configuration.md b/docs/webui_build_configuration.md
index cffae3f..dcb823a 100644
--- a/docs/webui_build_configuration.md
+++ b/docs/webui_build_configuration.md
@@ -205,9 +205,10 @@
                flaky build errors.
 manifest_excludes: List of input files to exclude from the output
                    the manifest file.
-enable_source_maps: Defaults to "false". Setting it to "true" turns on TS
-                    compiler's 'inlineSourceMap' and 'inlineSources' flags.
-                    Non-inlined source maps are currently not supported.
+enable_source_maps: Defaults to the value of the enable_webui_inline_sourcemaps
+                    GN flag. Setting it to "true" turns on TS compiler's
+                    'inlineSourceMap' and 'inlineSources' flags. Non-inlined
+                    source maps are currently not supported.
 ```
 
 #### **Example**