resource_sizes.py has been updated to print out resource sizes on a per-generated-header basis:
https://codereview.chromium.org/2692933004/

output from build/android/resource_sizes.py --min-pak-resource-size 100 out/Default/apks/Chrome.apk


                                                                          HEADER UNCOMPRESSED SIZE
                                           gen/chrome/grit/generated_resources.h     2.56m  36.83%
                                gen/components/strings/grit/components_strings.h     1.70m  24.54%
                                         gen/ui/resources/grit/webui_resources.h   610.10k   8.57%
                                      gen/components/grit/components_resources.h   557.80k   7.84%
                                  gen/content/app/strings/grit/content_strings.h   247.47k   3.48%
                               gen/blink/public/resources/grit/blink_resources.h   243.74k   3.43%
                                             gen/chrome/grit/browser_resources.h   222.67k   3.13%
                                               gen/chrome/grit/theme_resources.h   137.08k   1.93%
                                            gen/content/grit/content_resources.h   118.59k   1.67%
                                   gen/android_webview/grit/components_strings.h   116.98k   1.64%
                                                gen/ui/strings/grit/ui_strings.h   110.22k   1.55%
                                                                         unknown    94.92k   1.33%
                                         gen/chrome/grit/google_chrome_strings.h    83.09k   1.17%
                                       gen/chrome/grit/net_internals_resources.h    45.38k   0.64%
                  gen/components/strings/grit/components_google_chrome_strings.h    28.62k   0.40%
                               gen/components/grit/components_scaled_resources.h    26.26k   0.37%
                                            gen/ui/resources/grit/ui_resources.h    22.17k   0.31%
                         gen/blink/public/resources/grit/blink_image_resources.h    21.62k   0.30%
                           gen/device/bluetooth/strings/grit/bluetooth_strings.h    14.19k   0.20%
                                     gen/chrome/grit/quota_internals_resources.h    10.61k   0.15%
                                            gen/chrome/grit/renderer_resources.h     8.48k   0.12%
                                                    gen/net/grit/net_resources.h     6.98k   0.10%
                                      gen/chrome/grit/platform_locale_settings.h     6.46k   0.09%
                                 gen/chrome/grit/translate_internals_resources.h     4.45k   0.06%
                            gen/chrome/grit/task_scheduler_internals_resources.h     2.21k   0.03%
                                       gen/chrome/grit/invalidations_resources.h     2.20k   0.03%
                        gen/components/strings/grit/components_locale_settings.h     1.64k   0.02%
                                          gen/chrome/grit/webapks_ui_resources.h     1.47k   0.02%
                                       gen/ui/strings/grit/app_locale_settings.h     1.38k   0.02%
                          gen/chrome/grit/password_manager_internals_resources.h     1.18k   0.02%
                                               gen/chrome/grit/locale_settings.h       406   0.01%
                                              gen/chrome/grit/policy_resources.h       182   0.00%


From this list, I think we should look to see if we actually need theme_resources.h.
It also looks like webui_resources is larger than we'd require on Android

But mainly, I don't think the granularity here is great. We should make grit output some extra metadata so that will allow mapping symbols back to .grd files, and even .grdp files.