pattern: Add Chromium pak file (#474)

* Add Chromium pak file pattern

* Show aliases & fix brotli check bug

* Add decompressed size

* Add notes

* Add PakEncoding enum

patterns/chromium_pak.hexpat

@@ -0,0 +1,81 @@
+#pragma author East_Arctica
+#pragma description Chromium Pak File
+
+import std.core;
+import std.io;
+
+struct IndexEntry {
+    u16 id;
+    u32 offset;
+};
+
+struct AliasEntry {
+    u16 id;
+    u16 index;
+};
+
+struct ResourceView {
+    u32 i = std::core::array_index();
+
+    u16 id     = parent.entries[i].id;
+    u32 start  = parent.entries[i].offset;
+    u32 end    = parent.entries[i + 1].offset;
+    u32 length = (end >= start) ? (end - start) : 0;
+
+    u8 data[length] @ start;
+    
+    // pak_util.py implies that this may also be gzip with a header of 0x1f 0x8b
+    bool is_brotli = (length > 8 && data[0] == 0x1e && data[1] == 0x9b);
+    if (is_brotli) {
+        u8 magic[2] @ start;
+        u48 decompressed_size @ start + 2;
+        // TODO: If brotli decompression is added to ImHex, add it here.
+    }
+};
+
+struct AliasResourceView {
+    u32 i = std::core::array_index();
+    
+    u16 id = parent.aliases[i].id;
+    u16 idx = parent.aliases[i].index;
+
+    bool valid = (idx < parent.resource_count);
+    u32 start  = valid ? parent.entries[idx].offset : 0;
+    u32 end    = valid ? parent.entries[idx + 1].offset : 0;
+    u32 length = (valid && end >= start) ? (end - start) : 0;
+
+    u8 data[length] @ start;
+
+};
+
+enum PakEncoding : u8 {
+    binary = 0,
+    utf8 = 1,
+    utf16 = 2
+};
+
+struct Pak {
+    u32 version;
+    if (version == 4) {
+        u32 resource_count;
+        PakEncoding encoding;
+
+        IndexEntry entries[resource_count + 1];
+        ResourceView resources[resource_count];
+    } else if (version == 5) {
+        PakEncoding encoding;
+        padding[3];
+        u16 resource_count;
+        u16 alias_count;
+
+        IndexEntry entries[resource_count + 1];
+        AliasEntry aliases[alias_count];
+        ResourceView resources[resource_count];
+        AliasResourceView alias_resources[alias_count];
+    } else {
+        std::error("Unsupported pak version");
+    }
+};
+
+// Some pack files are stored gzipped and need to be gunzipped first
+Pak pak @ 0x00;