Apply snake_case to generated CharacterPropertyData.cpp

This CL has no behavior changes.

Bug: 770603
Change-Id: I2084d2a10cf69f2815c147769d46d8a5f0cba7ff
Reviewed-on: https://chromium-review.googlesource.com/961621
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542993}

third_party/WebKit/Source/platform/BUILD.gn

@@ -101,7 +101,7 @@ action("color_data") {
 compiled_action("character_data") {
   tool = ":character_data_generator"
   outputs = [
-    "$blink_platform_output_dir/CharacterPropertyData.cpp",
+    "$blink_platform_output_dir/character_property_data.cc",
   ]
   args = rebase_path(outputs, root_build_dir)
 }