Add doc note that <webview>.clearData's ClearDataTypeSet.cache is available m43+.

chrome/common/extensions/api/webview_tag.json

Index: chrome/common/extensions/api/webview_tag.json
diff --git a/chrome/common/extensions/api/webview_tag.json b/chrome/common/extensions/api/webview_tag.json
index 5485f6d0f01a43f7d4b2d11a4b0a1ab567d63bea..30603b0fe9480bd6bc8b28bf68ad9b5b74ab1838 100644
--- a/chrome/common/extensions/api/webview_tag.json
+++ b/chrome/common/extensions/api/webview_tag.json
@@ -30,7 +30,7 @@
         "description": "A set of data types. Missing properties are interpreted as <code>false</code>.",
         "properties": {
           "appcache": { "type": "boolean", "optional": true, "description": "Websites' appcaches." },
-          "cache": { "type": "boolean", "optional": true, "description": "The browser's cache. Note: when removing data, this clears the entire cache; it is not limited to the range you specify." },
+          "cache": { "type": "boolean", "optional": true, "description": "Since Chrome 43.<br>The browser's cache. Note: when removing data, this clears the entire cache; it is not limited to the range you specify." },
           "cookies": { "type": "boolean", "optional": true, "description": "The partition's cookies." },
           "fileSystems": { "type": "boolean", "optional": true, "description": "Websites' filesystems." },
           "indexedDB": { "type": "boolean", "optional": true, "description": "Websites' IndexedDB data." },