[Ext] Cosmetic code: Remove escaping " and \ in generated_schemas

Use raw string literals instead to avoid hurting readers' eyes (note:
no one should read them though). For example, this CL turns
const char kUsb[] = "{\"functions\":[{\"parameters\":[{\"$ref\":...
to
const char kUsb[] = R"R({"functions":[{"parameters":[{"$ref":...
in gen/extensions/common/api/generated_schemas.cc

This makes generated .cc file size slightly smaller: e.g. in linux cros
build, the sizes in bytes are (before->after):
gen/chrome/../apps/platform_apps/../generated_schemas.cc 14137 -> 12396
gen/chrome/../extensions/../generated_schemas.cc        426698 -> 367237
gen/extensions/../generated_schemas.cc                  369079 -> 318170
gen/extensions/shell/../generated_schemas.cc              1632 -> 1535

Note that this should not have any impact on binary size.

Bug: None
Test: None, no visible changes expected.
Change-Id: I432c510396ead6e86fae71f63a3e2c099420b485
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2133658Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755987}

tools/json_schema_compiler/cpp_bundle_generator.py

@@ -340,17 +340,16 @@ class _SchemasCCGenerator(object):
       json_content = json.dumps(_PrefixSchemaWithNamespace(
                                      _RemoveUnneededFields(api)),
                                 separators=(',', ':'))
-      # Escape all double-quotes and backslashes. For this to output a valid
-      # JSON C string, we need to escape \ and ". Note that some schemas are
+      # This will output a valid JSON C string. Note that some schemas are
       # too large to compile on windows. Split the JSON up into several
       # strings, since apparently that helps.
       max_length = 8192
       segments = [
-          json_content[i:i + max_length].replace('\\', '\\\\').replace(
-              '"', '\\"') for i in range(0, len(json_content), max_length)
+          json_content[i:i + max_length]
+          for i in range(0, len(json_content), max_length)
       ]
-      c.Append('const char %s[] = "%s";' %
-          (_FormatNameAsConstant(namespace.name), '" "'.join(segments)))
+      c.Append('const char %s[] = R"R(%s)R";' % (_FormatNameAsConstant(
+          namespace.name), ')R" R"R('.join(segments)))
     c.Append('}  // namespace')
     c.Append()
     c.Concat(cpp_util.OpenNamespace(self._bundle._cpp_namespace))